The aim of the study was to examine the relationships of obesity, lipids and apolipoproteins with the risk for subsequent ischaemic heart disease in middle-aged women, using a case-control study nested within a cohort study. A total of 3634 women aged 26-88 were recruited in Guernsey between 1977 and 1985 and followed until June 1986 by abstraction of their general practitioners' records. Fifty-one cases of incident ischaemic heart disease (11 myocardial infarction, 40 angina) were identified. For each case up to 4 controls were selected, matched for age and date at recruitment. Odds ratios for the development of ischaemic heart disease in the middle and upper thirds of the distribution for each variable in the controls, relative to the lowest third (and two-sided P-values for linear trends), were: 3.0, 2.6 (0.015) for Quetelet's index; 3.3, 5.1 (0.003) for total cholesterol; 0.5, 0.6 (0.102) for apolipoprotein A-I; 1.8, 2.4 (0.015) for apolipoprotein B; 1.3, 2.1 (0.155) for apolipoprotein(a). The increased risks associated with increased Quetelet's index and total cholesterol were independent of each other and these variables were more strongly related to myocardial infarction than to angina. The relationships of risk with serum cotinine, fatty acids, dehydroepiandrosterone sulphate and sex hormone binding globulin were weak and did not approach statistical significance.