According to studies on a variety of malignant tumors from different organs MUC1 mucin antigen presents as a valuable marker of cancer progression and prognosis. During recent years, a great number of monoclonal antibodies (mabs) directed to MUC1 was generated. Their epitopes can be classified according to their position within the tandem repeat domain of the mucin and with respect to effects exerted by site-specific glycosylation. In this study, eight mabs from different clusters were selected to correlate their epitope specificity with their binding pattern in human cancer specimens. By applying an immunohistochemical ABC-peroxidase method, ten carcinomas derived from breast, pancreas, stomach and colon were characterized. A positive reaction of all mabs could be observed in the majority of the carcinomas, however, the extent of the stained tumor area varied significantly. In general, mabs M38, VA1 and BC3 exhibited the strongest staining reaction. Mab BW835 showed a similar binding intensity, especially in pancreatic and gastric carcinomas. It is tempting to speculate that the different binding patterns may reflect differences in epitope specificity. In conclusion, future immunohistochemical, immunoserological and therapeutic studies involving MUC1 antigen should prefer well-characterized and highly reactive mabs detecting defined peptide epitopes.