Cell cultures from explants of the rabbit hydronephrotic kidney (HNK) cortex consisted of fibroblasts and an esterase‐positive cell that phagocytizes zymosan. Cortical cell cultures from the contralateral kidney (CLK) contained only the fibroblast. The HNK cultures exhibited an endotoxin‐induced prostaglandin (PG) E2(three ‐ fourfold) release indicative of the presence of macrophages, whereas no response was observed in the CLK cultures. At bradykinin concentrations as low as 10–9M there was a 20‐fold stimulation of PGE2from the HNK cultures and a sevenfold stimulation in the CLK cultures. The heterogeneous population of cells in the HNK cultures was separated using a mild trypsin treatment which permits passage of only the fibroblasts. The HNK‐passaged cultures contained no phagocytic cells and did not release PGE2in response to endotoxin. The passaged HNK cultures released less PGE2in response to bradykinin as compared to primary cultures and had a decreased cyclooxygenase activity as determined by exogenous arachidonic acid conversion to PGE2. Conditioned media from adherent rabbit peripheral blood mononuclear cells stimulated basal PGE2production (two ‐ threefold) from both the HNK and CLK cultures. These findings demonstrated the similarity of the PGE2production by cultured HNK cortical cells as compared to the ex vivo perfused HNK.