A prospective survey among 116 subjects native of Black Africa and residing in prison was carried on, in order to estimate the prevalence of parasitosis, HB Virus and HI Virus infections. These subjects, all males, were selected at random among Black Africans, which were representative of 6.5% of the prisoners in the prison of Fresnes. The average age and stay in France were respectively of 25.7 and 3.3 years. 34% had regular drug-habit (I.V. heroin intake for 8 subjects). 54% were carriers of parasites: 33 subjects for intestinal nematode (whipworm: 19; hookworm: 5; Strongyloides stercoralis: 5; ascaris: 3; pinworm: 1); 2 for filariasis (loaiasis: 1: onchocerciasis: 1); 11 subjects for bilharziosis and 43 carriers of intestinal protozoosis (mild form amebiasis principally); also, 11 scabies were noticed. By another way, 8 subjects (6.9%) were HIV1 +, and none HIV2+; 11 (9.5%) were HBs+. In relation to parasitosis, practical attitude hesitate between systematic evaluation of infections (more satisfying but expensive), systematic treatment (easier but less suitable), and prescription of well-fixed tests according to the conclusions of a specialized advice. In relation to virosis, a systematic serological determination is not justified for this population, in actual economical conditions, and because there is no specific treatment.