In this work we reported the results obtained using two ELISA-tests (the seropositivity was confirmed by Western-Blot) for detection of HIV-Ab in normal and at risk population (according by the classification from C.D.C. 1982) exposed to screening for various, sanitary measures. Our results concerning the percentage of seropositivity to HIV-Ab in drug-addicts (49%) are in agreement with the results obtained in the most qualified Italian Centres. The incidence of congenital infection is high, pointed 50%; the 100% of seropositive children were infected by drug-addicts seropositive parents. Casuistry among haemophilic patients we have demonstrated a greater seropositivity in B haemophilic subjects than A haemophilic ones. The seropositivity (24%) verified among prisoners is totally related to drug-addiction. Prevalence of seropositivity among heterosexual partners of HIV positive subjects was 22% among female partners of infected men, and 9% among male partners of infected women. Checking performed upon nursing staff who casually were contaminated by seropositive patient's blood confirmed 100% of seronegativity after eight months. No seropositive subjects were performed in every not a risk group.