The present investigation was performed to study the participation of the specific isozyme of mono-amineoxidase (MAO) during reserpine-modulated release of medullary catecholamines (CAM). This was carried out by pretreatments of pargyline and clorgyline followed by reserpine administration. The findings revealed that the pigeon adrenal contained predominantly MAO-A. Blockade of type B activity by pargyline caused a significant rise in adrenomedullary CAM content in reserpinized pigeons. However, clorgyline (an MAO-A inhibitor) administration followed by reserpine treatment showed no appreciable change in the medullary CAM level, suggesting that type B activity is mainly responsible for reserpine action on the adrenal medulla in the pigeon. In addition, reserpine was also able to decrease the glandular corticosterone content, while pargyline and clorgyline failed to alter this trend in reserpinized pigeons.