Using a silver staining technique, Nucleolar Organizer Region-associated proteins (NORs) were evaluated on paraffin sections of 16 resected prostatic adenocarcinomas stage A1. Then 30 histological areas was selected which comprised 6 areas for each grade of Prostatic Intraepithelial Neoplasia: PIN 1, PIN 2, PIN 3, 6 areas of normal glandular prostatic epithelium and 6 areas of well differentiated prostatic adenocarcinoma (Gleason I). The mean numbers of argyrophilic nucleolar organizer regions (AgNORs) increased from normal glandular prostatic epithelium to PIN 3, while the mean numbers of well differentiated prostatic adenocarcinoma was similar to PIN 1. A statistically significant difference (P less than 0.01) for AgNORs was found between normal glandular epithelium, PIN 1, PIN 2 and PIN 3 and between PIN 3 and well differentiated adenocarcinoma. It was concluded that AgNORs counts provide to significant kinetic evaluation of PIN and prostatic adenocarcinoma besides to supply a better definition of PIN.