The magnitude and effects of intrapopulational variability in the sizes of eggs produced by the salamanders Ambystoma maculatum, A. opacum, and A. tigrinum have been investigated by calorimetric and respirometric procedures. It has been found that some females produce eggs with as many as 29.0 cal while others in the same population at the same time produce eggs with as few as 16.5 cal. Significant differences in the dry weight-specific energy content of ova have been found at the species, population, and individual levels, but the contribution of this variability to the variability in total energy content of ova is relatively low. All embryos regardless of species or temperature use 1.45 cal in order to hatch. Development to the feeding stage is more efficient for embryos that develop from larger ova and at warmer temperatures, offering an explanation for altitudinal and latitudinal variation that is often seen in egg size in amphibians. The effects of a fluctuating temperature environment are shown to b...