Peripheral blood smears were examined for asymptomatic malaria parasitemia among 406 objectively healthy subjects in North Mara, Tanzania. A total of 33(8.1%) of subjects were found to have asymptomatic malaria parasitemia. Prevalence rates for parasitemia were highest among the youngest age groups and lowest in those 35 years of age and older. Of the 33 positive smears, 21 (63.6%) contained Plasmodium falciparum, 9(27.2%) plasmodium malariae and 3(9.2%) mixed infections of the two. General population surveys for asymptomatic malaria parasitemia in North Mara have shown much higher prevalence rates than those found in the present study. The lower prevalence rates in this study are accounted for by the fact that the population sample consisted of subjects determined to be healthy by objective criteria and lacking hepatomegaly and splenomegaly. The absence of splenomegaly and hepatomegaly in this group suggests that they represent a portion of the population who have already developed significant immunity levels to malarial infections.