The possible associations between Plasmodium falciparum malaria and HIV (human immunodeficiency virus) seropositivity were investigated in 1986 at the Mama Yemo Hospital in Kinshasa, Zaire. No significant difference was found in the HIV seropositivity rate of 164 children presenting with P. falciparum malaria (1.2%) and 169 healthy controls (0.6%). Secondly, no association was found between P. falciparum slide positivity (51.6%) and HIV seropositivity (3.8%) among 1046 children presenting to the hospital with medical complaints. Infants less than 6 months old had the lowest slide-positivity rate, but among infected children the younger ones more frequently had high parasitaemias. HIV seropositivity rates were highest for children less than 6 months old. In older children, seropositivity was strongly associated with a history of blood transfusion. Thus, in Kinshasa children, P. falciparum malaria is a major public health problem; perinatal transmission and blood transfusions constitute important mechanisms of HIV infection; and P. falciparum does not appear to act as an opportunistic agent in children infected with HIV.