693 IVDU (intravenous drug user) sera from Copenhagen, Malmö and Stockholm were tested, 247 retro- and 446 prospectively, for antibodies to human T-lymphotropic virus (HTLV), types I and II, by means of a commercial whole-virus EIA and/or an HTLV-I/-II peptide-based EIA. Positive EIA reactions were checked and typed by electrophoretic immunoblotting, a differential peptide-based EIA and nucleic acid amplification/hybridization with HTLV-I and -II specific primers and probes. 3 (0.7%) of the prospectively tested IVDUs from Malmö, none of 100 from Stockholm and none of 45 from Copenhagen were HTLV-seropositive. The 3 Malmö IVDU cases were a female immigrant from South America, her male native Swedish spouse (both HTLV-I), and a male immigrant Italian heroinist (HTLV-II). We conclude that HTLV was uncommon among intravenous drug users, a sentinel population, in Sweden and Denmark during 1986 and 1989. However, the occurrence of 3 HTLV-positive cases in Malmö 1993 indicates that the situation can change rapidly.