The effects of vasopressin, angiotensin II, and calcium ionophore A23187 were examined and compared on endogenous prostaglandin E2 (PGE2) production, in the absence of exogenous arachidonate, by glomeruli and cortical and medullary collecting tubules freshly prepared from rat kidney. Angiotensin II stimulated PGE2 production in the glomeruli but not in the collecting tubules. Vasopressin at concentrations which stimulate cAMP production in collecting tubules failed to stimulate PGE2 production in both glomeruli and collecting tubules. Significant stimulation of PGE2 production occurred in response to calcium ionophore A23187 in both glomeruli and collecting tubules. These results showed that vasopressin failed to stimulate PGE2 production from endogenous precursors in both glomeruli and collecting tubules of the rat kidney while angiotensin II stimulates PGE2 production in the glomeruli but not in collecting tubules. In addition, an ability to produce PGE2 may be greater in medullary than in the cortical portions of collecting tubules as judged by the response to calcium ionophore.