A survey on intestinal parasites in a rural area of Tanzania revealed the presence of eight protozoa and seven helminths in 287 subjects (81.8%). The prevalence of Entamoeba histolytica and Ascaris lumbricoides was higher in HIV-negative than in HIV-positive patients (P < 0.01; P < 0.04) (25.1% and 12.5% for E. histolytica; 10.5% and 3.7% for A. lumbricoides). On the other hand, Cryptosporidium parvum, Isospora belli and Strongyloides stercoralis prevalence was higher in HIV-positive than in HIV-negative patients (P < 0.01). The prevalence of these two opportunistic protozoa was also higher in AIDS patients than in HIV-positive patients without AIDS. Specific anti-C. parvum IgG were detected by ELISA in 18% and 56% of HIV-negative and positive patients, respectively, confirming the high number of contacts between this parasite and humans. Specific anti-Encephalitozoon cuniculi and anti-Encephalitozoon hellem IgG were detected by IFA in 18% and 19% of subjects, respectively, without any correlation with HIV and malaria infections.