Hypertriglyceridemia has frequently been found both in subjects with AIDS and in asymptomatic HIV-positive ones. In order to evaluate the importance of hyperlipemia as an index of the clinical evolution of HIV infection, the levels of triglycerides, total cholesterol and CD4 lymphocytes were determined over a period of 2 years in 8 haemophiliacs with AIDS, 13 asymptomatic HIV-positive and 45 HIV-negative haemophiliacs attending the Operative Unit of Coagulation Disorders of the University of Pisa. The mean concentration of triglycerides and incidence of hypertriglyceridemia were significantly higher in haemophiliacs with AIDS, compared with HIV-negative subjects (p<0.0001), while the triglycerides values of asymptomatic HIV-positives fell between those of the other groups. Cholesterol levels were lower in HIV-positive haemophiliacs and in those with AIDS compared with HIV-negatives. No correlation was found between triglyceride levels and those of CD4 lymphocytes.