AbstractThe oxygen consumption of various diapausing blastocysts from mammals having delayed implantation (mink, northern fur seal, black bear, armadillo and lactating rat) was studied with the Cartesian diver apparatus and compared with that of blastocysts from mammals where implantation is not delayed (rabbit, nonlactating rat). In general, there is a variation in the respiratory rate between species and within a species but the oxygen consumption of the delayed blastocysts was not different from the non‐delayed ones. It was concluded that the control of the delay in implantation in the animals studied, does not lie in the realm of respiratory changes.