• To determine the effect of growth hormone (GH) administration on growth rate, ultimate size, and glucose tolerance of intact rats, we administered ovine GH to male Sprague-Dawley weanling rats for six weeks. Growth hormone, in a dose sufficient to double the growth rate and increase sixfold the somatomedin C (SM-C) levels of hypophysectomized rats, failed to increase the rate of growth or size of visceral organs of intact rats. Their SM-C levels increased only 10%. Following glucose administration, the mean blood glucose levels were higher at every time point measured in those treated with GH compared with the Intact control animals. We conclude that, although there was no difference in somatic or visceral growth, the dose of exogenous GH administered increased SM-C levels and decreased glucose tolerance in the intact rats. While a larger GH dose might increase the final body size of non—GH-deficient animals, impaired glucose tolerance could be a significant side effect.