To explain the occurrence in salivary pleomorphic adenoma of structures with an arrangement and appearance of tumour cells resembling acini, two tumours showing such structures and, for comparison, a tumour showing goblet cells were examined with the use of histochemistry and immunocytochemistry for constituents of the salivary secretory process. One tumour consisted mainly of slightly granular cells with an acinar arrangement, which contained neutral and carboxylated glycoproteins, -SH groups and cytoplasmic epithelial membrane antigen. The second tumour showed a minor component of structures resembling mucous acini, which contained neutral and carboxylated glycoproteins, -SS- groups and fucoglycoconjugates. The goblet cells of the third tumour contained sulphated glycoproteins and were associated with cystic lumina. Acinar phenotypes in salivary pleomorphic adenoma could reflect either an unusual line of differentiation or luminal cells with increased synthesis and/or retention of variably mature glycoproteins different from those of goblet cells. Disordered secretion and externalization of glycoproteins are possible factors influencing phenotypes in this tumour.