The binding of peroxidase-conjugated Dolichos biflorus (DBA), Triticum vulgaris (WGA), Canavalia ensiformis (Con A), Arachis hypogaea (PNA), Lotus tetragonolobus, and Bandeiraea simplicifolia I (BSAI) to gastrointestinal carcinoid tumours was studied. The results indicate that carcinoid tumour cells express certain carbohydrates similar to those present in the adjacent surface epithelium. The differences in the lectin-binding properties of carcinoid tumours of different sites of the gastrointestinal tract are closely related to the regional differences in the lectin binding of adjacent surface epithelium. These observations therefore form a useful basis for further studies in the application of lectin histochemistry to elucidate the histogenesis of carcinoid tumours.