The incidence and patterns of argyrophilia in 25 endometrial carcinomas were analysed and correlated with other pathological features. In addition, the frequency with which argyrophilia was identified within nonneoplastic endometrium and cervix from this carcinoma group was compared with that of a control group of 25 patients without malignant disease. Using the Grimelius stain, argyrophilia was observed in 68% of endometrial carcinomas, although in 28%, only rare positive cells were identified. Seven tumours (six argyrophilic carcinomas and one small-cell undifferentiated carcinoma) were examined by electron microscopy, which revealed neurosecretory granules. Argyrophilia was also found at the ultrastructural level. ACTH and calcitonin were revealed by the immunoperoxidase technique in four of the nine argyrophilic tumours examined. Argyrophilic cells in nonneoplastic endometrium were found in 10% of the carcinoma cases and 8% of the control cases; this has not been described previously. No correlation could be established between the presence or degree of argyrophilia and histological type or grade of carcinoma, extent of tumour infiltration, or argyrophilia in nonneoplastic endometrium or cervix. We conclude that argyrophilia in endometrial carcinomas has no clinicopathological significance. The histogenesis of endometrial and cervical argyrophilic cells is discussed.