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In recent years the citadel of scientific medicine has been assailed by critics and no less passionately defended. Precious few contributors to this battle, however, have succeeded in offering a candid and considered account of its present strengths and weaknesses. For this reason Sir David Weatherall's reflections will be especially welcome. For many years professor of clinical medicine and currently regius professor of medicine at the University of Oxford, Weatherall can speak as an authoritative insider. But in no way does that make him a doctrinaire apologist for the medical establishment, or for the prevalent style of medical intervention.

Weatherall makes no bones about the limits to medicine's achievements. Many of this century's triumphs - the antibiotics revolution, the global eradication of smallpox - have been the completion of breakthroughs achieved long before (eg Pasteurian bacteriology). The most dazzling bedside medicine and surgery of recent years - he instances by-pass surgery and other cardiological advances - have at bottom been what he bluntly calls "patch-up medicine": keeping ailing people going, without radically curing them, and at spiralling costs in money, manpower and resources.

Infectious diseases declined in the 19th century - more, Weatherall concedes, thanks to better living conditions than through direct medical intervention; and since then progress has been sluggish and partial in overcoming the gravest of afflictions: cancer, heart attacks, strokes, mental disorder, parkinsonism and other neurological deficits - and much else too from Aids down to the common cold. Despite therapeutic improvements, certain disorders, for instance, asthma and diabetes, continue to spread, and pathogens develop resistance to antimicrobial drugs. Nor does the third-world situation offer cause for joy, as traditional diseases, like malaria, defy eradication programmes and first-world diseases (cancer, etc)worsen with westernisation. Aware of the shortcomings of orthodox medicine, and finding it reductionist and dehumanised, patients shop around, trying alternative therapies, some potty, some plausible. And who can blame them? comments Weatherall.

Yet all is not gloom. Modern medicine has brought myriad genuine and significant advances, of which Weatherall discusses numerous instructive examples in a lucid layman's guide to contemporary medical science. Major improvements - like the conquest of pernicious anaemia or the introduction of insulin for diabetes - have come through fruitful co-operation between numerous different branches of inquiry: basic science, clinical investigations, epidemiology, pharmacological research, with much credit being due to the crucial introduction of the clinical trial, which belatedly replaced subjective speculation with objective proof.

But with such complexity, clinical science can possess no foolproof method, no guaranteed success. Skill, genius, serendipity and sheer luck must combine in ways that defy formulae. Therein lies some of the explanation why medicine today risks being hoist by its own petard. Over the years it has fuelled goldrush expectations of instant results - how else was it to secure funding? Little wonder then that the public, or the Exchequer, experiences disillusionment with the god that only partly succeeded.

So what is to be done? In part Weatherall recommends soldiering on, with no expectation of magic breakthroughs. In large measure, medical advance has depended on improvements in basic science (that is, research undertaken for curiosity's sake, without a specific application in mind). That long-term strategy must continue, particularly in promising fields like cell and molecular biology and genetics, which Weatherall discusses at length. History suggests that the pressures being exerted in the present economic climate for more narrowly utilitarian approach to research would prove a false economy.

But Weatherall also believes that medicine needs to shake itself up and change direction. Modern "patch-up" medicine is getting prohibitively expensive without, in the end, actually improving health very dramatically. Medicine presently spends most of its energies swabbing up the kitchen floor because the tap is leaky and the sink is blocked. It would make more sense to shift attention from symptom management to addressing causes. More scientific research is needed to discover that root causes of disease; epidemiology will highlight why certain people get sick and not others. And, Weatherall stresses, far more needs to be done to stop people falling ill in the first place. Refreshingly, so far as this reviewer is concerned, he calls for heightened concern for what he terms the "environmental" sources of illness (including lifestyle), with a view to prevention.

Sickness is not some biological constant: its incidence differs widely according to wealth, class, education, occupation and other social variables. The spectacular (if again belated) success of postwar epidemiology, associated with Richard Doll, Austin Bradford Hill and others, in identifying the prime cause of lung cancer has delivered into our hands an easy and cheap way of virtually eliminating at a stroke a disease which is estimated to cause two million deaths a year worldwide: the ending of smoking. Not every disease will prove to have a " smoking revolver" as conspicuous as the cigarette, but until we redouble our research, we will remain in the dark.

If comparable resources went into discovering the causes of diseases, and promoting prevention, as go into fixing sick people up, ours would be a far healthier population. Not only that, but, as Weatherall wisely observes, therein might lie the only strategy for rescuing medicine from the "spiralling costs and limited resources" malady which threatens to prove incapacitating.

Health costs escalate while returns appear to be diminishing. All concerned with the resolution of this bewildering dilemma will profit from Weatherall's frank and provocative discussion, and may be relieved to find that senior scientists are aware of the urgent need for medicine to scrutinise its priorities and maybe change its orientation.

Roy Porter is professor of the social history of medicine, Wellcome Institute, London.