It has previously been shown that plasma radioimmunoassayable growth hormone (GH) falls following exposure to cold. This response was examined in the normal, adrenalectomized, thyroparathyroidectomized, and adrenalectomized-thyroparathyroid-ectomized rat to determine the effects of the absence of corticosterone (B) and of the thyroid and parathyroid glands on this response. GH decreased from a high prestress level to a low poststress level in both the normal and adrenalectomized animal. The thyropara-thyroidectomized and the adrenalectomized-thyroparathyroidectomized rats had a low prestress GH level, which was not decreased further following cold exposure. The prestress B levels were higher in the thyroparathyroidectomized animals than in the normal. Poststress levels of B were similar in both groups. It appears that an intact thyroid and/or parathyroid gland is necessary to maintain the normal resting plasma levels of GH and B, whereas stress levels do not appear to be affected.