Tissue sections from 80 human breast carcinomas have been examined for evidence of binding of the two fucose-specific lectins, Lotus tetragonolobus and Ulex europeus I, with enzymes utilized as an indicator system. Both single-staining and double-staining methods (Lotus tetragonolobus-peroxidase and Ulex europeus I-alkaline phosphatase) have been employed. In contrast to normal breast in which there is consistent reactivity of all epithelium with Lotus tetragonologus a variable loss of binding has been found within carcinomas. Surprisingly, this bears no relationship to tumour differentiation; nor does it correlate with local lymph node metastasis. Ulex europeus I has a variable reactivity with carcinomas, as it does with normal breast epithelium, and this likewise has no correlation with differentiation. However, a relationship has been found between specific patterns of binding and axillary lymph node status. The value of using two lectins with the same major sugar specificity but having different binding affinities is illustrated in this study, in which differences in behavioural characteristics have been identified between fucose-containing glyco-conjugates having minor structural variations.