Three different extracts and four alkaloids from the root bark of Cryptolepis sanguinolenta have been assessed in vitro against Plasmodium falciparum D-6 (chloroquine-sensitive strain), K-1, and W-2 (chloroquine-resistant strains). Cryptolepine (1) and its hydrochloride (2), 11-hydroxycryptolepine (3), and neocryptolepine (5) showed a strong antiplasmodial activity against P. falciparum chloroquine-resistant strains. Quindoline (4) was less active. The highest activity was obtained with compound 1. In vivo tests on infected mice showed that cryptolepine (1), when tested as its hydrochloride (2), exhibited a significant chemosuppressive effect against Plasmodium berghei yoelii and Plasmodium berghei, berghei, while 1 had the same effect against P. berghei yoelii only. Compounds 3 and 4 did not show activity in this in vivo test system.