The causes of the excess coronary heart disease (CHD) risk in South Asian migrants from the Indian subcontinent remain unclear. Comparisons of CHD risk factors amongst South Asian migrants living in Britain with those of the general UK population provide only a partial explanation. We compared Gujaratis in Britain with similar, non-migrant Gujaratis in India, to test the hypothesis that differences in CHD risk factors associated with migration would be more informative. Randomly sampled Gujaratis aged 25-79 years living in Sandwell (n = 242) were compared with age-, gender- and caste-matched contemporaries remaining in their villages of origin in Navsari, India (n = 295). Lifestyle indices, food intake and physical activity, were assessed with standardised questionnaires and energy expenditure and metabolic parameters measured. British Gujaratis had higher, mean body mass indices by 6 (4.5-7.4) kg/m(2) mean (95% CI), and greater dietary energy intake, fat intake, blood pressure, fasting serum cholesterol, apolipoprotein B, triglycerides, non-esterified fatty acid (NEFA) and C-reative protein concentrations than Gujaratis in India. Dietary folate and serum folate and Vitamin B(12) were lower and plasma homocysteine was higher in India. Smoking was less prevalent and high-density lipoprotein cholesterol tended to be higher in Britain. Diabetes prevalence was high in both populations and impaired fasting or 2 h post-glucose challenge plasma glucose was even more prevalent in Gujarat. In India, however, where insulin secretion and NEFA were lower diabetes and impaired glucose tolerance were less frequently accompanied by excess metabolic CVD risk factors. In conclusion, exposure to increased fat intake and obesity related to migration is likely to explain the disproportionate combination of established and emerging CHD risk factors prevalent in Gujaratis in Britain. Strategies to improve nutrition and to identify and treat cardiovascular risk factors such as dyslipidaemia and hypertension are urgently required.