Primary cultures of smooth muscle cells (SMCs) were derived from the human prostate obtained from four patients with symptomatic benign prostatic hyperplasia (BPH) undergoing open prostatectomy, using collagenase digestion and preferential adhesion techniques. SMCs attached to the plastic substrate by 6 to 10 h, proliferated by 2 to 3 days, and reached confluency by 10 to 14 days with a "hill-and-vallery" pattern. Immunocytochemical staining of cultured SMCs using anti human muscle-specific actin monoclonal antibody (HHF35), confirmed that more than 90% primary cultured cells were positive for HHF-35. Transmission electron microscopy of SMCs revealed dense myofibrils (6-8 nm width) showing focal density, and was compatible to smooth muscle cells. This primary culture will be utilized to provide a useful model to investigate the character of smooth muscle cells and their role in the development of BPH.