The alkaloid content of ten identified and three unidentified species of Haemanthus was investigated. Five new alkaloids—coccinine, manthidine, manthine, montanine, and natalensine—were isolated and characterized. Tazettine was the major alkaloid in H. albiflos, and trace amounts of lycorine were found in H. coccineus. All isolated alkaloids are optically active and contain a methylenedioxy group attached to an aromatic ring (confirmed by a positive Labat's test). Their ultraviolet spectra show two characteristic maxima (240–244 mμ and 294–297 mμ), similar to tazettine (a known alkaloid with a methylenedioxyphenyl group). Coccinine, montanine, and natalensine are isomers with the molecular formula C₁₇H₁₉NO₄, each featuring a methylenedioxy group, one hydroxyl, and one methoxyl function. The minor alkaloids manthine and manthidine are isomers with the formula C₁₈H₂₁NO₄. Among the abundant alkaloids, montanine and natalensine exhibit slight hypotensive activity.