In mammals, medetomidine causes reliable sedation and can be quickly and smoothly antagonized by atipamezole, allowing smooth and rapid recovery. However, doses of up to 1 mg/kg of medetomidine reportedly do not immobilize avian species. In this study, the sedative and cardiopulmonary effects of medetomidine administered intramuscularly was evaluated in 2 dosage groups (1.5 mg/kg and 2 mg/kg) of 4 domestic pigeons (Columba livia) each and 2 dosage groups (1.5 mg/kg and 2 mg/kg) of 2 yellow-crowned Amazon parrots (Amazona ochrocephala ochrocephala) each. Ten minutes after medetomidine injection, the reflex score of anesthetic level was determined in each bird, and the heart and respiratory rates were measured while birds were manually restrained. Results were compared with values obtained before sedation and 5 minutes after atipamezole injection. Although all birds showed signs of sedation, a desired reflex score for sedation was not obtained in all birds. The reflex score of sedation in domestic pigeons receiving 2 mg/kg medetomidine was not significantly lower than that of birds receiving 1.5 mg/kg, indicating no increase in sedation with the higher dose. However, the Amazon parrots that received the higher dose had a significantly lower reflex score than those that received the lower dose, indicating an increase in sedation with the higher dose. In both species and at both doses, a decrease in heart rate and in respiratory rate were observed, with no significant differences between the groups. Antagonism with atipamezole at both 2.5 and 5 times the medetomidine dose caused a smooth, rapid, and complete recovery. In these 2 species, although medetomidine did have a sedative effect and was reliably antagonized, it did not reliably induce a desirable state of sedation, even at the high doses investigated. Therefore, medetomidine alone as an anesthetic agent is not recommended for routine use in avian practice.