HTLV-1 was the first human retrovirus to be isolated. It has been shown that it is the causative agent of T cell leukemia in the adult and some types of subacute myelopathies. The virus is transmitted by similar routes as the AIDS virus. HTLV-1 infection is endemic in South Japan, the Caribbean countries and some African areas. The prevalence of HTLV-1 infection in our country is unknown in the general population and in the groups at high risk. We report the preliminary results of a study of 1279 serum samples from high risk individuals from the Barcelona area. ELISA and Western blotting were used to detect antibodies. We found evidence of anti-HTLV-1 only in 4 of 905 (0.44%) parenteral drug abusers and in 1 of 102 western Africans. Anti-HTLV-1 were not found in the remaining sera from 62 homosexuals, 53 patients with leukemia and/or lymphoma, 3 with idiopathic spastic paraparesis and 154 with multiple blood transfusions. These results suggest that HTLV-1 has a very low diffusion in our area. The 4 positive heroin addicts are the first reported in our country with evidence of HIV and HTLV-1 coinfection.