Qualitative changes of glycoconjugates in luminal surface and goblet cell mucin from colon mucosa of 1,2-dimethylhydrazine (DMH)-treated rats were studied. Eight fluoresceinated lectins were used: Dolichos biflorus (DBA), Glycine max (SBA), Triticum vulgare (WGA), Limax flavus (LFA), Arachis hypogaea (PNA), Griffonia simplicifolia-I (GS-I), Ulex europaeus-I (UEA-I) and Canavalia ensiformis (Con A). The lectin-binding patterns were studied in tumors arising in proximal and distal portions of the colon, in transitional mucosa (TM) and in mucosa distant from tumors. Lectin reactivity observed in mucosa of DMH-treated rats was compared with that obtained in colon mucosa of control rats. In tumors and non-neoplastic mucosa of DMH-treated rats the reactivity of DBA, SBA, WGA, LFA, GS-I and Con A were similar to that in the mucosa of control rats. In contrast, important changes were observed in the reactivity of UEA-I and PNA. Contrary to the staining in the control mucosa, UEA-I bound intensely to all carcinomas and PNA to 50% and 60% of carcinomas arising in proximal and distal colon, respectively. Moreover, in TM and mucosa distant from tumors, UEA-I and PNA also differed in their binding patterns to that obtained in the colonic mucosa of the control rats. UEA-I- and PNA-binding to luminal surface and UEA-I-binding to the mucin of distal colonic mucosa from DMH-treated rats was similar to that observed in rat fetal colon suggesting a reappearance of a fetal-type pattern. Contrarily, PNA-reactivity in goblet cell and carcinoma mucin is a unique feature of colonic carcinogenesis not present during fetal development.