African medicinal plants provide a rich source of biologically-active natural products. By the use of simple bioassays in conjunction with an approach involving bioactivity guided fractionation, it is possible to isolate novel compounds with interesting properties. Several hundred plant extracts have been submitted to different screens, including bioautography on TLC plates with the fungi Cladosporium cucumerinum and Candida albicans. Among the other test systems are a bioassay for molluscicidal activity with the schistosomiasis-transmitting snail Biomphalaria glabrata and a benchtop assay for larvicidal activity with larvae of the mosquito Aedes aegypti, the vector of yellow fever. Using a variety of modern separation techniques, a number of compounds with activity in these bioassays have been isolated. These include prenylated xanthones, tetracyclic phenols and saponins. The role of saponins and saponin-containing plants in the control of schistosomiasis is outlined.