1. This investigation was undertaken to compare pre- and postjunctional receptors involved in the responses of the canine mesenteric and pulmonary arteries to angiotensin II. 2. In the mesenteric artery, angiotensin II caused an enhancement of tritium overflow evoked by electrical stimulation (EC30% = 5 nM), the maximal effect representing an increase by about 45%. Postjunctionally, angiotensin II caused concentration-dependent contractions (pD2 = 8.57). Saralasin antagonized both pre- and postjunctional effects of angiotensin II, but it was more potent at post- than at prejunctional level (pA2 of 9.51 and 8.15, respectively), while losartan antagonized exclusively the postjunctional effects of angiotensin II (pA = 8.15). PD123319 had no antagonist effect either pre- or postjunctionally. 3. In the pulmonary artery, angiotensin II also caused an enhancement of the electrically-evoked tritium overflow (EC30% = 1.54 nM), its maximal effect increasing tritium overflow by about 80%. Postjunctionally, angiotensin II caused contractile responses (pD2 = 8.52). As in the mesenteric artery, saralasin antagonized angiotensin II effects at both pre- and postjunctional level and it was more potent postjunctionally (pA2 of 9.58 and 8.10, respectively). Losartan antagonized only the postjunctional effects of angiotensin II (pA2 = 7.96) and PD123319 was ineffective. 4. It is concluded that in both vessels: (1) pre- and postjunctional receptors belong to a different subtype, since they are differently antagonized by the same antagonists; (2) postjunctional receptors belong to AT1 subtype, since they are blocked by losartan but not by AT2 antagonists; (3) prejunctional receptors apparently belong to neither AT1 or AT2 subtype since they are blocked by neither AT1 nor AT2 antagonists.