We examined the staining pattern of various lectins in the malignant and benign prostatic tissues to clarify the difference of sugar residues of mucosubstances between them. The binding of different lectins (Concanavalia ensiformis [Con A], Triticum vulgaris [WAG], Ricinus communis [RCA-I], Arachis hypogaea [PNA], Ulex europaeus [UEA-I], Glycine max [SBA], and Gliffonia simplicifolia II [GSA-II]) to cells of benign prostatic tissues (17 cases) and adenocarcinoma (54 cases) was evaluated immunohistochemically. SBA which was negative in benign epithelial cells, showed tendency to the binding to prostatic carcinoma (42.6%). UEA-I was significantly bound to the adenocarcinoma (68.5%) compared to the benign prostatic tissue (35.3%). We also examined histochemically 25 pairs of tissues obtained from prostatic adenocarcinoma before and after the various therapies with various lectins. The histological responsiveness on the post-therapeutic specimens showed a significant correlation to the clinical responsiveness to therapy. But the staining pattern of these 7 lectins on the pre-therapeutic specimens did not show a significant correlation to the clinical responsiveness to therapy. In summary, the staining pattern of some lectins in the prostatic cancers is different from that in the benign prostatic tissues.