In this study, we have investigated the effect of caloric intakes in 15 subjects (9 males and 6 females ranging in age from 48 to 66) and the effect of P/S (polyunsaturated/saturated) fat ratio in 9 subjects (7 males and 2 females aged from 50 to 64) on HDL-C, total cholesterol (TC) and triglyceride (TG) levels in plasma. All subjects were selected from inpatients with low HDL-C level (<45mg/dl). In the first study (Fig. 1), the subjects were placed on 20-25 Cal (per kg of ideal body weight), 25-30 Cal and 30-35 Cal test diets containing almost constant amount of protein and fat. Each subjects was given one of the test diet for 14-17 days with interval. The order of the diet was randomized. P/S fat ratio of the diet was maintained between 1.0 to 2.0 and daily cholesterol content was 0.3 to 0.7g. When compared to the control, HDL-C was raised (p<0.01) by 20-25 Cal and 25-30 Cal diets. TG was lowered (p<0.05) by 20-25 Cal diet. Hypocaloric diet containing less than 30 Cal with medium P/S ratio shows to offer the advantage with respect to HDL-C and TG metabolism. In the second study (Fig. 2), the test diets of different P/S fat ratio from 0.3-0.7, 1.0-2.0 and 3.0-4.0 were respectively administered for 14 days. The diets were isocaloric (20-30 Cal per kg of body weight) and contained 0.3-0.9g of cholesterol. The diet with the lowest P/S fat ratio was initially administered, medium and then the highest one continued with no interval. All subjects lost the weight during the test. HDL-C was increased (p<0.01) by the diets with medium and the highest P/S fat ratio. Also the highest P/S ratio diet reduced (p< 0.05) TC level. Though the increment of HDL-C was observed, it was possibly due to the ef-fect of limited caloric intake provided by the test diet. Accordingly the effect of polyunsa-turated fat on HDL-C remained to be clarified.