The more plausible hypotheses regarding the mechanism which controls amphibian embryonic respiration have been reviewed, providing some explanation for the contradictory respiratory ratios between intact and homogenized eggs reported by other investigators.The concentration of embryonic material appears to be of the utmost significance in the relative rates of respiration of homogenized as compared to intact eggs. A close correspondence between increased oxygen uptake and the ATPase activity resulting from homogenization has been demonstrated. This would account for the lack of respiratory effect by 2,4-dinitrophenol which has been described in homogenized eggs of Rana pipiens and Bufo arenarum. Homogenization, as well as 2,4-dinitrophenol could stimulate oxygen uptake by altering the ATP/ADP ratio. By means of ATPase inhibition it has been also demonstrated that the respiration of homogenates is strongly affected by ADP while exogenous ATP is almost without effect.