Bioassay-guided fractionation of extracts of Toddalia asiatica, a plant used by the Pokot tribe of Kenya to treat fevers, has yielded the alkaloid nitidine as the major antimalarial component. Fractions containing nitidine have in vitro 50% inhibitory concentrations against Plasmodium falciparum in the range of 9 to 108 ng/ml for a range of chloroquine-susceptible and -resistant strains. The results show a lack of cross-resistance between chloroquine and nitidine.Although malaria is in principle preventable and curable, in practice the majority of the population at risk cannot pay for modern treatment and the disease remains a major cause of childhood mortality in the developing world. Recent results with the vaccine sPf66 show a mean protective effect of only 30%, with very wide confidence limits (1). The rapid spread of resistance to chloroquine and related quinoline-based antimalarial agents has greatly increased the risk of malaria to many rural populations, so that there is an urgent need for affordable treatment. One possible source of such treatment lies in the traditional herbal remedies used by ethnic groups, but treatment with these remedies has suffered from a number of deficiencies. Diagnosis is often a problem, identification of plant material may be insecure, and the chemical content of extracts may vary considerably. We have set out to overcome these barriers to effective treatment by systematically evaluating the effectiveness of some of the remedies used by an ethnic group of Kenyan farmers.The Pokot traditionally inhabit a highland plateau, west of the Rift Valley in Kenya. However, the present study concerned a group of Pokot who live on Ol Ari Nyiro Ranch, Laikipia, Kenya, a plateau to the east of the Rift Valley, and who have previously been described in some detail (5).In interviews, the Pokot herbalist Cheptosai Selale, who is 90 years old, described the use of 26 plants for the treatment of malaria and fever, of which only 14 were available at the time of collection (see Table 1). Two of the 14 plants produced extracts with significant antimalarial activity against laboratory strains of Plasmodium falciparum. Bioassay-guided fractionation of the extract from Toddalia asiatica gave a pure alkaloid, nitidine, which has potentially useful antimalarial activity. MATERIALS AND METHODSPlant material. Plant material was collected from Ol Ari Nyiro Ranch and was botanically authenticated by Christine Kabuye and Joshua Muasya of the Herbarium, National Museums of Kenya, where voucher specimens were deposited. Information provided by the herbalist included the required part of the plant, the precise locality for collection, and the time when curative potency was maximal. Plant material for study was dried at room temperature, pulverized, and stored dry in plastic bags until extracts were obtained.Preparation of aqueous crude extracts for preliminary analysis. Aqueous crude extracts (10%) were prepared in a manner analogous to that used by the herbalist. Powdered plant material (10 g) was weighed in...