The effect of a three-phase multifactorial institution-based rehabilitation programme on coronary heart disease (CHD) risk factors was studied in an open randomised trial comprising 228 patients undergoing coronary artery bypass surgery allocated into a rehabilitation (R) group (n = 119) and a hospital (H = control) group (n = 109). Follow-up examinations were performed at 6 and 12 months. Serum total cholesterol and triglyceride levels decreased significantly in both groups during follow-up. These decreases were not significantly different between the R and H groups. Serum high density lipoprotein (HDL) cholesterol level increased significantly at 6 and 12 months in the R group, but not in the H group. The differences in the changes between the groups were not significant. The ratio of serum HDL cholesterol to total cholesterol increased significantly in the R group from the preoperative value of 0.154 to 0.179 (P less than 0.001) at 6 months and to 0.180 (P less than 0.001) at 12 months. In the H group these values were 0.152, 0.166 (P less than 0.001) and 0.168 (P less than 0.001), respectively. The significance of the differences in the changes between the groups were P = 0.01 at 6 months and 0.06 at 12 months. These differences were more obvious in patients aged 55 years or under. There was a significant decrease (P = 0.005) in the proportion of smokers in the R group and a significant increase in the proportion of patients taking regular exercise in both groups as assessed by questionnaire.(ABSTRACT TRUNCATED AT 250 WORDS)