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In our biological screening of higher plants, an aqueous and an 80% EtOH extract from the root bark of Cryptolepis sanguinolenta showed potent antibacterial, anticomplementary, and moderate antiviral activities, but no antifungal effect could be detected. Bioassay-guided fractionation of the 80% EtOH extract led to the isolation of three alkaloids: quindoline (1), hydroxycryptolepine (2), cryptolepine· HCl (3), and the corresponding base cryptolepine (4). All compounds strongly inhibited the growth of Gram-positive bacteria (MIC≤ 100 µg/ml) and showed a moderate (MIC= 125 or 250 µg/ml), a weak (MIC= 500 µg/ml), or no activity (MIC> 500 µg/ml) against selected Gram-negative bacteria. They also possessed a bactericidal effect depending on the bacterial strain. Compounds 1, 2, and 3 displayed a dose-dependent inhibitory effect on the classical pathway of the complement system while compounds 2 and 3 …