The activity and mass of lipoprotein lipase (LPL) in postheparin plasma (PHP) from patients with hypertriglyceridemia coupled with hypertension, impaired glucose tolerance, hyperinsulinemia were investigated in order to clarify the cause of hypertriglyceridemia and the effects of bezafibrate (CAS 41859-67-0), a novel lipid lowering agent. Eight weeks of treatment with bezafibrate (200 mg/d) lowered plasma total cholesterol and triglyceride by 7 and 39%, respectively, and increased plasma high density lipoprotein (HDL) cholesterol by 23% in the patients (n = 15). The LPL activity and mass of PHP in the patients were found to be lower than in the normal controls. The LPL activity and mass of PHP in the patients before treatment with bezafibrate (n = 15) were 2.05 +/- 1.06 mumol/ml/h and 147 +/- 45 ng/ml, respectively, whereas after treatment with 200 mg/d of bezafibrate for 8 weeks, these values were 3.62 +/- 1.30 mumol/ml/h (p < 0.01) and 226 +/- 57 ng/ml (p < 0.05), respectively. The increases of LPL mass were positively correlated with the decrease of triglyceride levels during the same period. These results suggest that the expression of LPL enzyme protein is impaired in patients with hypertriglyceridemia coupled with hypertension, impaired glucose tolerance and hyperinsulinemia, and the impaired expression of LPL recovers during treatment with bezafibrate, resulting in improvement of hypertriglyceridemia.