To better understand direct and indirect androgen action on rat prostatic growth and function, the various cell populations within the intact adult ventral, dorsal, and lateral prostate lobes were characterized for the presence or absence of androgen receptor (AR). Polyclonal rabbit antibodies raised against amino acids 1–21 of the rat AR (PG-21) were used in combination with a library of monoclonal antibodies directed against cell-specific antigens for positive cellular identification. Luminal epithelial cells were strongly AR positive, with an order of ventral > lateral ≥ dorsal. In the lateral lobe, staining intensity was strongest in the peripheral regions, whereas a similar gradient was not apparent in the ventral and dorsal prostate. Basal epithelial cells were AR negative in all regions of the three lobes. Periacinar smooth muscle was strongly positive for AR, and this staining did not vary with the thickness of the muscle layer. Endothelial cells of the vasculature were AR negative, while the perivascular smooth muscle cells were AR positive. The majority of stromal fibroblasts were AR negative, although a number of AR-positive fibroblastic-appearing cells were observed within the ventral and dorsal lobes. Staining with ED2, a specific marker for tissue macrophages, revealed that fixed macrophages were present in significant quantities in the stroma of intact rat prostate lobes. Since these were frequently identified as AR positive, macrophages may partially account for the appearance of AR-positive stromal cells. Thus, the present findings indicate a complex pattern of AR expression among different cell types of the three prostate lobes. Cells types that express AR can potentially be considered as direct targets of androgen action, whereas those lacking AR should be considered as indirect targets or androgen-insensitive cells. (Endocrinology129: 3187–3199,1991)