Asian immigrants to England and Wales have high mortality from coronary heart disease but low mortality from colon cancer. A survey of Asians in the London boroughs of Brent and Harrow was undertaken with the object of investigating this. Compared with the British population, the Asians consumed less saturated (S) fat and cholesterol and more polyunsaturated (P) fat and vegetable fibre. The P/S ratio of the Asians' diet was 0.85 compared with 0.28 in the British population: this was reflected in the very high linoleic acid content of their plasma lipids. The plasma total cholesterol and high-density-lipoprotein cholesterol of Asian men was similar to that of a British comparison group; the concentrations in Asian women were much lower than in British women. Smoking rates were low in both Asian men and Asian women. The high rates of coronary heart disease in Asian immigrants are not explained by the levels of these risk factors.