Plasma levels of vitamin E (vit E) and polyunsatured fatty acids of phospholipids (PUFA-PL) as well as erythrocyte glutathione peroxidase (GSH-Px) activity are significantly lower (p less than 0.001) in patients HIV sero-positive (AIDS and ARC cases) both affected and not affected with seborrheic dermatitis and in 32% of HIV sero-negative intravenous drug abusers (IVDA, A subgroup) than in controls. The deficiency of PUFA-PL (mainly C20:3 n-6, C20:4 n-6 and C22:6 n-3) which is associated with a significant increase (p less than 0.001) of saturated palmitic and stearic acids and monounsaturated oleic acid, cannot be correlated to an active lipoperoxidative process. In fact the levels of thiobarbituric acid-reactive materials (TBA-RM) are not increased in the plasma of HIV sero-positive patients and A subgroup of IVDA. It is likely that the reduction of PUFA-PL is due to an inhibition of hepatic microsomal desaturase enzymes (delta 6 desaturase, delta 5 desaturase, delta 4 desaturase) which are involved in both n-6 and n-3 pathways. Since IVDA represent, and not only in Italy, a major risk category for HIV infection, we suggest that reduced blood levels of vit E, GSH-Px and particularly PUFA-PL may be added to the list of risk factors favouring the onset and the development of AIDS.