Serum total cholesterol, triglycerides, high density lipoprotein cholesterol, low density lipoprotein cholesterol, apolipoprotein A-I and apolipoprotein B were evaluated as potential indicators of the risk of coronary artery disease in young (less than 46 years) normocholesterolaemic, non-diabetic men who had previously sustained a myocardial infarction (n = 50) and in healthy age and sex matched controls (n = 122) with a similar socioeconomic background. Significant differences were observed between patients and controls in the mean concentrations of serum total cholesterol, triglycerides, low density lipoprotein cholesterol, high density lipoprotein cholesterol and apolipoprotein B, as well as in the ratios of total cholesterol to high density lipoprotein cholesterol and apolipoprotein A-I to apolipoprotein B. No significant difference was demonstrated in the concentration of apolipoprotein A-I between the two groups. Stepwise discriminant analysis indicated that apolipoprotein B was the best discriminant between patients and controls. The percentage of exact classification was 74% in patients and 66% in controls. When the patients were compared to a subset of controls (n = 50) matched for age and total cholesterol, significant differences were demonstrated only in the mean concentrations of apolipoprotein B. Discriminant analysis confirmed that the best single discriminating variable was apolipoprotein B. The results therefore indicate that in young normocholesterolaemic, non-diabetic Indian men with myocardial infarction, apolipoprotein B is superior to other lipid parameters studied, as a marker for coronary artery disease.