The form of malaria caused by Plasmodium falciparum is probably the most important infectious disease of man. In tropical Africa alone, where malaria affects almost the entire population, it has been estimated that every year the disease causes the death of 1 million children under 14 yr old1. The mosquito vector of malaria is infected when it ingests mature gametocytes in blood taken from a human carrier of the disease. Development of the parasite continues in the mosquito and culminates with the sporozoite stage, which initiates a new infection when injected by the mosquito into a further human host. Research on P. falciparum sporozoites has been severely limited by a general lack of availability of suitable patients with gametocytes. It was hoped that the recently developed continuous cultivation of P. falciparum2 would solve this, as gametocytes are often produced during cultivation. However, we and others soon found that these gametocytes failed to mature in culture3,4, or at best did so only rarely and unpredictably5–7. We report here that addition of hypoxanthine to the culture medium permits the production of mature, infectious P. falciparum gametocytes on a regular basis.