The activities of hepatic and lipoprotein lipase and the levels of lipo- and apoproteins were compared in two groups of normoglycaemic men representing the highest (n = 18) and lowest (n = 15) fasting insulin quintiles of first degree male relatives of non-insulin-dependent diabetic patients. The high insulin group representing insulin-resistant individuals had significantly lower post-heparin plasma lipoprotein lipase activity than the low insulin group (14.2 +/- 4.0 vs 20 +/- 5.8 mumol NEFA.ml-1.h-1, p < 0.001); hepatic lipase activity did not differ between the two groups (24.2 +/- 11 vs 18.0 +/- 5.3 mumol NEFA.ml-1.h-1, NS). The lipoprotein lipase/hepatic lipase ratio in the high insulin group was decreased by 66% as compared to the low insulin group (0.75 +/- 0.57 vs 1.25 +/- 0.65, p < 0.01). In the high insulin group both total and VLDL triglycerides were higher than in the low insulin group (1.61 +/- 0.57 vs 0.86 +/- 0.26 mmol/l, p < 0.001 and 1.00 +/- 0.47 vs 0.36 +/- 0.16 mmol/l, p < 0.001, respectively) whereas HDL cholesterol and HDL2 cholesterol were lower (1.20 +/- 0.30 vs 1.43 +/- 0.22 mmol/l, p < 0.05 and 0.49 +/- 0.21 vs 0.71 +/- 0.17 mmol/l, p < 0.05, respectively). Total cholesterol, LDL cholesterol or HDL3 cholesterol did not differ between the two groups. The mean particle size of LDL was smaller in the high insulin group than in the low insulin group (258 +/- 7 vs 265 +/- 6 A, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)