Neutral and acid mucins and eosinophil and argyrophil crystalloids were studied in the glandular intraluminal contents of 130 prostatic carcinomas (PCa) and 22 atypical adenomatous hyperplasias (AAH). Specimens were studied in the usual extension for diagnostic purposes and considered positive when minimal amounts of mucin or any crystalloid were present. Some amount of altered secretion was seen in 110 PCa (84.6%) and in 17 AAH (77.3%); the similarity of the figures speaks for the close relationship of these lesions. The relative incidences in PCa/AAH were 61.5%/77.3% for neutral mucin, 80%/54.5% for acid mucin (p < 0.01), 25.4%/50% for eosinophil crystalloids (p < 0.02), 44.6%/9.1% for argyrophil crystalloids (p < 0.01) and 57%/36% for a compound secretion. The incidence of eosinophil crystalloids was greater in AAH and inversely proportional to the Gleason grade in PCa. The incidence of acid mucins and argyrophil crystalloids was higher in PCa and directly proportional to the tumour grade in all but the poorly differentiated ones. It is therefore suggested that AAH positive for acid mucins or argyrophil crystalloids be classified in the high grade AAH group.