The epidemiology of retrovirus HTLV-II is scarcely known even though it appears to be narrowly related to parenteral drug addiction. In order to find out the prevalence of HTLV-II among IVDU in our area, the sera of 137 subjects who came to our center for clinical evaluation were analyzed. The presence of HTLV-I/II antibodies were determined via ELISA and the sera that were repeatedly reactive were confirmed by the Western blot technique which reveals infection by both retroviruses. Two sera were repeatedly positive by ELISA (1.45 percent). Western blot confirmed HTLV-II positivity in both sera. Serology for HIV-1 was positive in 52 sera (37.9%). The two HTLV-II positive sera were also positive for HIV-1. These results indicate that HTLV-II infection is already present in the IVDU population in our area, where, similar to what happens in the U.S. and Europe, this retrovirus is implicated in the majority of HTLV infections in IVDU.