Although there have been extensive studies of serum lipid levels in psoriasis, the data are conflicting. In the present study, 38 male psoriatic patients and 40 age-matched male control subjects were studied. In addition, a 75 g oral glucose tolerance test (OGTT) was performed in 28 patients and 28 age-matched control subjects, in order to exclude subjects with abnormal OGTT values from the study. Twenty-two patients and 26 control subjects had normal OGTT values. There was a tendency for psoriatic patients with normal glucose tolerance to have increased triglyceride levels, but this was not statistically significant. Total cholesterol and high-density lipoprotein-cholesterol levels in patients were normal. However, serum apo B (P < 0.005), C-II (P < 0.005) and C-III (P < 0.005) levels in patients were significantly elevated compared with control subjects. When control subjects and patients with abnormal OGTT values were also included, a significant increase in triglyceride and apo E levels, and a significant decrease in the apo A-I level were observed in psoriatic patients. These findings suggest that psoriasis per se is associated with increases in apo B, C-II and C-III levels, but that this does not profoundly affect lipid levels. The abnormal lipoprotein metabolism may be related to the high incidence of atherosclerosis in psoriasis.