Effects of lowering serum triglyceride levels were investigated among 44 el derly hypertriglyceridemic patients with risk factors for stroke, reduced cere bral perfusion, and a history compatible with symptomatic occlusive cerebro vascular disease. Patients were randomly assigned to either treatment with gem fibrozil, a lipid-lowering agent, or control conditions. Subjects in both groups were instructed to follow a diet recommended for lowering serum lipid levels, while the treatment group was additionally administered 600 mg daily of gemfi brozil. Subjects assigned to the treatment group (n = 22) showed significant re ductions in serum triglyceride levels (p < .0005). Control subjects (n=22) did not show any significant changes in serum triglyceride levels. There were also no significant changes in total cholesterol levels in either group. Analyses of values for mean bihemispheric gray matter cerebral blood flow measured by the xenon 133 inhalation method and cognitive scores tested by the Cognitive Ca pacity Screening Examination indicated that gemfibrozil-treated patients main tained significantly higher levels of cerebral perfusion and cognitive perform ance than untreated controls did. Regression analyses for different treatment intervals indicated that both cerebral blood flow and cognition showed linear improvements that correlated directly with the duration of treatment. Lowering triglyceride levels in hyperlipidemic subjects appears to benefit cerebral perfu sion and cognitive performance after four to six months.