A series of 56 cases of prostatic adenocarcinoma and 48 cases of benign prostate hyperplasia were studied with histochemical, immunohistochemical methods and Feulgen-Image Analysis Technique. Duct-acinar dysplasia (DAD) was found in 81.8% of the prostate adenocarcinoma cases collected, but only in 47.9% of the benign hyperplasia cases. The frequency and extent of disruption of basal cell layer increased coincidently with the progressive increase of DAD grading. Intraluminal acid mucin and metachromasia stained with toluidine blue around the acini were identified in DAD. Immunohistochemical staining for prostatic acid phosphatase, cytokeratin, vimentin and UEA-1 receptor changed in DAD cells. The nuclear areas, DNA content and ploidy, mean numbers of AgNOR in DAD cells were higher than those in benign hyperplasia of the prostates and lower than those in adenocarcinomas, which indicates the possession of premalignant behavior of prostatic carcinoma.