An alkaloid, dioscorine, has been isolated from various species of yam of the family Dioscoreaceae. Pinder1 has summarized the history of this, confirmed its molecular formula as C₁₃H₁₉O₂N and has documented certain of its chemical and physical properties2. A similar alkaloid has been extracted from a further species common in the wild state in Nigeria and identified by its botanical characteristics and typically small starch grains as Dioscorea dumetorum (Yoruba name, esúru3). The latter alkaloid has not been obtained crystalline, but has been extracted and purified by various procedures; together with its crystalline salts, its analysis supports the formula C₁₃H₂₁O₂N. Its infrared and ultra-violet spectra differ from those reported for dioscorine. Thus the D. dumetorum alkaloid shows a single absorption maximum at 2080 A. on a calibrated 'Unicam' spectrophotometer as compared with a maximum at 2170 A. reported for dioscorine. The chemistry of the former is being further investigated. When injected into mice, the alkaloid of D. dumetorum acts as a convulsant poison. The convulsions are usually clonic at first, later tonic and may be followed either by death or recovery. When injected by the intra-peritoneal route, using a freshly prepared 1 per cent aqueous solution, the LD50 is approximately 65 mgm. kgm. Concentrations of 10⁻⁵ reduce the response to acetylcholine on the isolated guinea pig ileum and isolated rabbit duodenum preparations. At a dose-level of 20 mgm./kgm. the responses of the cat's blood pressure to acetylcholine and to adrenaline are altered. The depressor effect of the former is reduced, and the pressor effect of the latter is enhanced. No local anesthetic effect could be demonstrated. Dioscorine2 apparently lacks atropine-like properties in the concentrations mentioned above, nor does it potentiate the action of adrenaline on the cat's blood pressure.