Antibodies reactive with retroviral gag proteins have been detected in patients with systemic lupus erythematosus (SLE). We investigated the immune responses against human immunodeficiency virus (HIV) 1 antigens in the sera of 44 Turkish patients with SLE. Serum samples were tested by using two different commercial enzyme immunoassay (EIA) kits and by Western blotting. EIA studies revealed positive results in 12 patients (27%) for HIV-1 antigens by one of the kits that coated with purified viral antigens. Immunoblot analysis showed antibodies mainly to retroviral gag proteins in 23 patients (52%). The most frequent reactivity was against the p18 gag protein (n = 9). Although antibodies reactive particularly with p24 antigen were described in the previous reports, antibodies to p24 were found in only two patients. These findings might reflect a serologic diversity in different ethnic groups and also suggest the involvement of different triggers in the etiopathogenesis of SLE.