The effect of temperature on the oxygen consumption of the eggs of four marine invertebrates, Strongylocentrotus purpuratus, Dendraster excentricus, Urechis caupo and Cioma intestinalis, was investigated. With Strongylocentrotus eggs the measurements were made in the early cleavage and gastrula stages as well as continuously up to the gastrula stage and at the temperatures 20°, 15°, 10°, and 7.5° C. With Dendraster eggs the measurements were made in the early cleavage, blastula and gastrula stages as well as continuously throughout those stages and at the temperatures 25°, 22°, 20°, 15° and 12° C. With Urechis eggs the measurements were made in the early cleavage stages and at the temperatures 22°, 20°, 15,° and 12° C. With Ciona eggs the measurements were made in the early cleavage stages and up to hatching and at the temperatures 20° and 15° C. In all cases, with the exception of one run with Dendraster, the total oxygen consumed during the same developmental period at the different temperatures is the same within the limits of error of the measurements. The exceptional Dendraster experiment showed a somewhat higher total respiration at 25° as compared with that at 15° C. Omitting this case, which needs to be further investigated, it may be concluded that at least in the range of temperatures investigated no optimum exists at which development is accomplished with a minimum oxygen consumption.