Prevalence and determinants of HIV infection were assessed in 313 parenteral drug addicts admitted to five Centers for Drug-Addict Assistance and two prisons located in the northeast of Italy (Friuli Venezia-Giulia), an area some distance from the major Italian cities first reached by the AIDS epidemic. The overall prevalence of HIV positivity was also rather high in this area, ie 30% with 24-36% confidence interval. The most important risk factors (besides syringe sharing applicable to all drug addicts), turned out to be of a geographical nature, ie living in Pordenone province (where a US military base is located) or coming from other endemic areas and having travelled long distances in the past three years. Prostitution also seemed to increase the risk of infection, but duration of drug addiction had little effect. In addition to persistent generalized lymphadenopathy (closely linked to HIV infection), reversal of helper:suppressor T-cell ratio was found in 67% of HIV positive individuals, but also in 31% of HIV negative ones. Clinical signs and symptoms strongly linked with HIV positivity were fatigue, weight loss, splenomegaly, fever and nocturnal sweats.