Seven simple indole bases—viz., N,N‐dimethyltryptamine (I), its Nb‐oxide, harmine (II), harmaline (III), (+)‐Nb‐methyltetrahydroharman (IV), (+)‐tetrahydroharmine (V), and (+)‐5‐methoxytetrahydroharman (VI)—were isolated from the leaves and stems of Banistereopsis argentea Spring ex Juss (Malpighiaceae) and their identity established by physical and chemical methods. In addition to these alkaloids, two partially characterized minor indole‐3‐alkylamines, together with choline and betaine, were obtained from the same parts of the plant. This was the first demonstration of the occurrence of Nb‐methyltetrahydroharman in the family Malpighiaceae and of a 5‐methoxytetrahydro‐β‐carboline alkaloid in nature. The total alkaloids from the leaves have shown three main pharmacological actions: nonspecific spasmolytic action against acetylcholine‐, histamine‐, and serotonin‐induced spasm; histamine release‐mediated depressor response; and pronounced behavioral effects.