The long-term influence of n-3 polyunsaturated fatty acids (n-3 PUFAs) on serum lipids and glucose homeostasis was studied in a group of non-diabetic, moderately hypertriglyceridaemic patients undergoing coronary artery bypass grafting. They were investigated according to the same procedure before and 6 months after the operation. Following randomization postoperatively, 28 patients received 3.4 g eicosapentaenoic and docosahexaenoic acid per day, whereas 29 patients comprised the control group. The decline in serum triglycerides after 6 months was significantly greater in the n-3 PUFA group than in the control group (median decline, -33.2% vs. -11.1%, p = 0.002), while no group difference was noted in serum total, HDL, or LDL cholesterol levels. Fasting plasma glucose levels decreased less in the n-3 PUFA group compared with the control group (median change, -0.2 mmol l-1 vs. -0.5 mmol l-1, p = 0.054). The corresponding changes in fasting insulin levels were -2 mIU ml-1 in the n-3 PUFA group and no change in the control group (p = 0.039). In both groups combined, the recorded changes in serum triglyceride and serum insulin levels were negatively correlated with the change in serum phospholipid n-3 fatty acids (r = -0.35, p = 0.008 and r = -0.32, p = 0.016, respectively). An oral glucose tolerance test revealed no significant group differences after 6 months, neither in the peak levels, nor in the areas under the curves between 0 and 3h after the glucose load for glucose, insulin, and C-peptide.(ABSTRACT TRUNCATED AT 250 WORDS)