An aqueous decoction of the root bark of Uapaca nitida Mull-Arg. is currently used locally at the Benedictine Mission at Peramiho in Tanzania to treat malaria. We have now demonstrated that extracts of root bark and leaves of this tree are active against the multidrug-resistant K1 strain of Plasmodium falciparum in vitro. An ethanolic extract of root bark showed activity against P. berghei in mice but at a dose which also showed toxic effects. The use of this plant in treating malaria appears to be novel and further studies would be of value.