Body and organ weights of 24 newborn dogs and 35 newborn cats were studied. All of the measurements, except weights of hypophysis, spinal cord and testes are larger in the dogs. As percentages of body weight, the organs are more equally divided, with seven organs relatively heavier in the dogs and eight in the cats. All except two of the measurements of the newborn dogs are more variable than in the newborn cats.

All of the organs are significantly correlated with body weight in the dogs and all except one, in the cats. All 15 of the organs are significantly correlated with body length in the dogs and 13, in the cats. The intercorrelations of the organ weights are somewhat higher in the dogs.

The coefficients of variation of the newborn are compared with similar coefficients in adult dogs and cats. Body weight, body length and the kidneys are more variable in the adult dogs and the other organs, so far as data are available, are more variable in the newborn dogs of both sexes. Seven organs are more variable in adult male cats and three in females. The newborn dog is more variable in body and organ weights than the newborn cat, but weights of body and organs are better correlated in the newborn dog than in the newborn cat.