The respiratory tract contains numerous peptides secreted from special pulmonary epithelial cells which are called endocrine cells. The function of neuroendocrine cells is modulated by amines. Serotonin has strong vasomotor and bronchomotor effects in the airway mucosa. The objective of this study was to determine presence and distribution of serotonin-positive endocrine cells in respiratory tract of goat and bovine via PAP (peroxidase anti-peroxidase) technique. As a result, while serotonin-immunoreactive cells were found in glands of larynx and bronchial epithelium in bovine, no positive cells were detected in goat. The present study suggests that the distribution of serotonin-immunoreactive cells may show differences between both respiratory tract regions and mammalian species.