The purpose of this study was to determine if exercise ameliorates the elevated levels of triglycerides in diabetic rats and also to determine if the capacity of liver to synthesize glycerides correlates with changes in plasma triglyceride levels. Forty female rats were divided into four groups: sedentary control, sedentary diabetic, exercised control, and exercised diabetic. Diabetes was induced by intravenous injection of alloxan (40 mg/kg), and control rats were sham-dosed with physiologic saline. All rats remained sedentary in their cages for the first week after the injections. The exercised groups were exercised for seven consecutive days for 2 h/d at 20 m/min (0 grade). All rats were killed 24 hours after the last exercise bout. Blood glucose levels were significantly higher in the diabetic group than the nondiabetic counterparts, but exercise did not affect glucose levels in either the diabetic or nondiabetic groups. Exercise, however, significantly lowered plasma triglyceride and free fatty acid levels in both diabetic and nondiabetic rats. The activities of the five enzymes involved in fatty acid synthesis were all depressed in the diabetic rats compared to controls, and exercise had no effect on the activities of the enzymes. The capacity of liver to synthesize total lipids, diglycerides, or triglycerides was not different in the diabetic rats from that of nondiabetic rats, and exercise did not change that. Only phospholipid synthesis from glycerol-3-phosphate was affected by diabetes. It is concluded that exercise ameliorates the elevations in plasma triglyceride levels that result from diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)