Several types of metaplasia can occur in human bladder epithelium under certain pathological conditions. We investigated 65 cases of cystitis, associated with different types of metaplasia, for the presence of endocrine cells, using histochemical and immunocytochemical methods. Tissues were obtained at cystoscopy and were routinely fixed in 10% buffered formalin. Endocrine cells were demonstrated, between the epithelial cells, in 40 out of 50 cases of cystitis glandularis or cystica. These cells were positive by the Grimelius' silver impregnation technique and were immunoreactive for protein gene product (PGP 9.5), a new general neuroendocrine marker, chromogranin and serotonin. No endocrine cells were detected in any of the specimens of normal epithelium nor those showing squamous metaplasia. Eighteen of these cases showed prominent nerve bundles in the subepithelial tissue, as revealed by PGP immunoreactivity.