Pirifibrate was given to 53 patients with type IIa, IIb or IV hyperlipoproteinemia (HLP), and the results of the first three months of treatment were evaluated. Patients in the study had cholesterol and triglyceride plasma levels higher than 300 mg/100 ml and 200 mg/100 ml, respectively, after following a diet without any pharmacological treatment for one month. After treatment with pirifibrate, mean plasma levels of cholesterol fell about 20% in types IIa and IIb HLP; triglycerides fell between 30% and 46% in types IIb and IV HLP. Slight increases in alpha-lipoproteins in the three types of HLP were measured. Prebeta-lipoprotein levels fell considerably in types IIb and IV. The variations observed in beta-lipoprotein levels were significant only in type IV, which initially showed low values.