Benign hyperplastic and neoplastic human prostate tissue samples were obtained by needle biopsy, transurethral resection or open prostatectomy. Acinar cells of both types of tissues were examined in the scanning electron microscope. It had been reported previously that adenocarcinoma acinar cells were more heterogeneous in size and shape than BPH acinar cells; the purpose of this study was to determine if there were surface morphology differences between the two types of tissues. Acinar cells were found to be extremely heterogeneous in their surface morphologies; three major types of surface morphologies were present - microvillous, ruffled, and bare. Within each class of surface morphology there was heterogeneity, both in size and density, of surface structures present. Microvillous, ruffled, and bare cells appeared to be present in normal, BPH, and neoplastic acini with no significant qualitative or quantitative differences in surface morphologies. Infrequently, it was possible to distinguish between well-differentiated and poorly-differentiated carcinomas because cells of the latter tissues were present in sheets rather than acini and appeared flat and totally devoid of surface detail. The SEM studies also sought to determine a marker to establish the origin of prostate tissue culture cells as normal, BPH or cancerous. Surface morphologies from tissues could be traced into the tissue cultures; again, three types of cells are present - bare, microvillous, and ruffled. However, since surface morphology does not appear to be a distinguishin feature of the pathology of the tissue it cannot provide a distinguishing marker for the origin of tissue culture cells. Scanning electron microscopy also provided an opportunity to observe possible secretory mechanisms and products in the prostate acinar cells.