To relate health to length of residence in the United Kingdom in an age-controlled sample of British South Asians, a cross-sectional survey was undertaken with interviews and physical measures in a two-stage stratified random cluster sample in the City of Glasgow. The sample consisted of 159 South Asians aged 30-40, with a mean age of 35 years (73.6 per cent of those invited). The main measures considered were body structure, lung function, pulse and blood pressure, history of physical and mental health, results of standardized questionnaires on mental health, angina and respiratory health, recent and past symptoms, history of accidents and sickness behaviour. It was found that over a quarter of the health measures showed differences by length of residence, and long-established residents had almost consistently worse results. More were overweight, reported heart trouble and respiratory conditions, had had accidents, experienced symptoms, especially respiratory and psychosomatic, needed glasses and took time ill in bed. Comparisons with North Indian data make it unlikely that these results are explained by positive selection of recent migrants. Also, the results do not endorse the assumption that the UK environment has promoted higher levels of health in migrants longer exposed to it, nor that the stress of the move promotes higher levels of illness in recent migrants. Further investigation is required of ways in which the UK environment, or the particular situation of South Asians within it, may be damaging to health.