The distribution of various tissue antigens was studied in mucoepidermoid carcinomas (n = 74) and acinic cell carcinomas (n = 38) by means of immunocytochemistry. Mucoepidermoid carcinomas were generally positive for cytokeratin and showed double expression for cytokeratin and vimentin in 31.1% and triple expression for cytokeratin, vimentin and GFAP in 24.1%. CEA was studied using new monoclonal antibodies which distinguish between epitopes that are present on CEA alone and those which are present on nonspecific cross reacting antigens as well. The monospecific CEA antibody was completely negative in mucoepidermoid carcinomas, while nonspecific cross reacting antigens (NCAs) were positive in mucoepidermoid carcinomas to a varying degree. Alpha 1-antichymotrypsin, a marker formerly thought to be specific for tissues for histiocytic origin, was positive in 85.1% of mucoepidermoid carcinomas. Twenty three percent of mucoepidermoid carcinomas showed focal infiltration by S-100 positive dendritic stromal cells, tumour cell being negative. Leu-M1 antigen was positive in 58.1% of mucoepidermoid carcinomas. Acinic cell carcinomas were generally positive for cytokeratin and in single cases showed double expression for cytokeratin and vimentin and triple expression for cytokeratin, vimentin and GFAP. Monospecific CEA antibody positivity could be demonstrated in 24.2% of acinic cell carcinoma, while nonspecific cross reacting antigens (NCAs) were positive in acinic cell carcinomas to a varying degree. Alpha 1-antichymotrypsin was positive in 97.4% of acinic cell carcinomas. 2.5% of acinic cell carcinomas showed focal infiltration by S-100 positive dendritic stromal cells, 2.5% of acinic cell carcinomas were positive for S-100 protein with no dendritic stromal cells present. Leu-M1 antigen was positive in 86.8% of acinic cell carcinomas. For S-100 protein and Leu-M1, no correlation with the clinical course, as reported previously for other tumours, could be observed.