Background: Little is known about the prevalence of infections in different population groups in Africa, and about the influence of living conditions on the spread of infections. This study is the first of its kind in the state of Eritrea and is expected to serve as an evaluation of the situation in the country. Objective: A serosurvey for human immunodeficiency virus (HIV), hepatitis B virus (HBV) and hepatitis C virus (HCV) was carried out during the summer of 1995 in Massawa, a small sea port in Eritrea (East Africa) in four groups considered to be at risk for these infections. Study design: The study subjects were former Guerrilla Fighters, Female Sex Workers, Truck Drivers, and Port Workers. Participants from a tribe called Rashaida were believed to be at low risk, and thus served as a control. Results: The Female Sex Workers had the highest incidence of HIV-1 infection, 29%, compared to 10% for Port Workers, and 3% for Guerrilla Fighters. On the other hand presence of HBsAg, indicating a high prevalence of hepatitis B carrier status, was highest in the Guerrilla Fighters, followed by the Rashaidas, and lowest in the Female Sex Workers. The Female Sex Workers were further tested for antibodies against HBV and the results revealed that 53% of them, 5%, had antibodies against HBcoreAg. Excluding the possibility of an acute infection at sampling time, three of them became HBsAg carriers. Surprisingly, our group of Truck Drivers did not show HIV-1 infection, and no HIV-2 infections were seen in the whole cohort. Conclusion: The study shows that the described groups have different prevalences of infection with HIV, hepatitis B and C which can partly be explained by their living conditions. (C) 1998 Elsevier Science B.V. All rights reserved.