A lectin was isolated from root tubers of winter aconite (Eranthis hyemalis) by affinity chromatography on fetuin-agarose, and it was partially characterized with respect to its biochemical, physicochemical and carbohydrate-binding properties. The Eranthis hyemalis lectin is a dimeric protein (Mr 62000) composed of two different subunits of Mr 30000 and 32000, held together by disulphide bonds. It is especially rich in asparagine/aspartic acid, glutamine/glutamic acid and leucine, and contains 5% covalently bound carbohydrate. Hapten inhibition assays indicated that the winter-aconite lectin is specific for N-acetylgalactosamine. In addition, the lectin exhibits a pronounced specificity towards blood-group-O erythrocytes. The winter-aconite lectin is the first lectin to be isolated from a species belonging to the plant family Ranunculaceae. It appears to be different from all previously described plant lectins.