Objective: This study was performed to investigate the difference in the serum-cholesterol- and triglyceride-lowering activities between phytosterols dissolved in diacylglycerol (PS/DG) and dispersed in triacylglycerol (PS/TG). The effects of the solvent on the concentrations of serum beta -sitosterol and campesterol were examined. Design: The study had a randomised crossover design. Subjects: Twelve healthy normocholesterolemic or moderately hypercholesterolemic men aged 29-50 y participated in this study. Interventions: For 2 weeks before the test period (designated as the control period), all subjects consumed control mayonnaise (PS free) daily with supper and were randomly assigned to two groups for the 2 week test period; one group was given mayonnaise containing PS (500 mg/day) dissolved in DG (10 g/day), and the other mayonnaise containing PS (500 mg/day) dispersed in TG (10 g/day). After a wash out period consuming control PS-fret mayonnaise for 4 weeks, the groups were reversed for 2 weeks. Results: PS/TG feeding had no effect on the serum cholesterol level. In contrast, PS/DG feeding significantly reduced the total and LDL cholesterol levels from the initial value of 5.57 to 5.31 mmol/l (4.7%, P < 0.05) and from 3.69 to 3.39 mmol/l (7.6%; P < 0.05), respectively. Moreover, the degree of total cholesterol reduction induced by PS/DG feeding in the test period was significantly greater than that induced by PS/TG feeding (P < 0.05). In addition, the serum beta -sitosteral and campesterol concentrations did not change juring the PS/TG or PS/DG feeding periods. Conclusions: Dissolution of PS in DG had a better serum cholesterol lowering effect than dissolution in TG. Sponsorship: Kao Corporation.