The development of resistance to insecticides by anopheline mosquito vectors of malaria and of resistance to drugs by Plasmodium falciparum pose new challenges for malaria control programs. The establishment of methods for the continuous cultivation in vitro of plasmodia provided an important new tool for research into the cellular biology and metabolism of these parasites. The molecular basis of the parasite's attachment to and entry into erythrocytes in the host is being elucidated. The impact of the intracellular parasite on erythrocyte metabolism is being explored, and the recognition of the role of plasmodia as an oxidant stress suggested a molecular basis for certain forms of genetic resistance to malaria. In addition, the consequences of parasitization are being studied with regard to alterations in erythrocyte antigenicity, rheologic properties, and the transport of nutrients and antimalarial drugs. The host's immune response to malaria is being assessed with regard to both protective and immunosuppressive effects. The rapid accumulation of new knowledge of host-parasite biology could provide the basis for the design of novel pharmacologic and immunologic methods for the control of malaria.