Rats with lesions of the dorsomedial nucleus of the hypothalamus (DMN-L) are hypophagic and have reduced linear growth and body weight, but normal body composition. Male Sprague-Dawley rats (170–190 g) housed individually under a 12:12 L:D schedule with lights out at 1430 hr received jugular cannulas, and on return to precannulation body weight (4.2±0.6 days), they received bilateral electrolytic DMN-L or sham-operations (SHAM). Rats with DMN-L (n=8) were hypophagic postsurgery and weighed less ( p<0.05) than SHAM at six days postlesion surgery. The difference in body weight between the two groups continued to expand over the next four weeks. Six days postsurgery, the rats were bled (RBC's returned in 10% BSA-saline) every 15 minutes between 0600–1215 hr and growth hormone (GH) subsequently assayed. The total GH secretion, as computed from the area under each rat's ultradian pattern, was similar in both groups (DMN-L versus SHAM, 2952.2±346.5 versus 2950.4±337.5). Using the PULSAR computer program, the baseline secretion (12.2±4.0 versus 11.8±2.7 ng/ml), total number of peaks (2.4±0.4 versus 2.4±0.2), and interpeak interval (2.8±0.5 versus 2.7±0.4, hr) were not significantly different between the DMN-L and SHAM rats, respectively. These data show that the growth-retarded DMN-L rat does not have a deficiency in total growth hormone secretion or an altered ultradian pattern, at a time when their body weight is diverging from the sham-operated controls. These data give further support to the previously suggested concept of a DMN-L reduced change in body weight ‘set-point’ or the alteration of an, as yet, undefined growth factor.