Light microscopic and histochemical changes in normal human prostate and benign prostatic hyperplasia (BPH) during long-term explant culture were characterized. Normal human prostate obtained at immediate autopsy of young adults or BPH obtained at the time of surgery were maintained in explant culture as long as 24 weeks. Morphologic alterations in glandular epithelium and stroma in response to culture conditions were assessed by light microscopy and histochemistry of mucosubstances. The histologic and histochemical responses of normal prostate and BPH to in vitro conditions were essentially identical. Within 1 week, secretory epithelial cells became necrotic and sloughed into acinar lumina. Remaining epithelial cells proliferated, repopulated acinar structures, and migrated onto explant surfaces forming a new well-differentiated epithelium characterized by synthesis and secretion of neutral and acidic mucosubstances. During subsequent periods in vitro, synthesis and secretion of mucosubstances gradually diminished whereas the stroma and deep glandular structures became necrotic. Our observations suggest that cells comprising the new epithelium in cultured explants of normal human prostate and BPH are derived from prostatic basal cells.