Sera collected between 1978 and 1985 from 716 parenteral drug-addicts admitted to our Clinic with viral hepatitis were tested for antibodies to HTLV III. None of the patients was showing symptoms suggestive of LAV/HTLV III infection at the time of sera collection. Positivity for HTLV III antibody was found and confirmed (by ELISA) in 212 subjects (29.6%). The earliest positivity appeared in a serum sample collected in February 1979. These and other data point to Milan as to the actual source of the Italian PDAs-linked LAV/HTLV-III epidemic.