Growth hormone (GH) content of pituitaries from rats with extensive ventral hypothalamic damage was determined by bioassay using the tibial epiphysial width stimulating test. Decrease in growth rate (measured by body weight and body length), decrease in pituitary size and decrease in pituitary somatotrophin concentration were produced by the lesion. It was estimated that the amount of GH per pituitary was reduced to approximately 15% of the normal. Secondary lesion-induced deficiences of thyroxine, testosterone or of vasopressin were not the cause of this effect because adequate replacement treatment was given. An earlier study on GH content of pituitaries from adrenalectomized rats was cited which makes it unlikely that lesion-induced ACTIi deficiency was the cause of low GH found in these experiments. The demonstration of low concentrations of GH in the pituitaries of rats with lesions is the first direct evidence that some phase of somatotrophin secretion (decreased synthesis or increased release or both) is affected by hypothalamic damage. Specificity of the effect remains to be established because the lesions which were used to interfere with growth and to lower pituitary GH involve a substantial portion of the primary plexus of the hypophysial-portal vessels.