The effect of frequency of growth hormone (GH) administration on longitudinal bone growth and body weight was studied in hypophysectomized rats. Replacement therapy with 3 different doses of human GH [(hGH) Crescormone] was started 10-14 days after hypophysectomy and was continued for 5 days. Longitudinal bone growth, as measured by the tetracycline method, and body weight were determined during the injection period. With a daily replacement dose of 128 micrograms of hGH body weight gain and longitudinal bone growth were significantly higher when the hormone was injected 4 and 8 times per day compared with animals receiving the hormone in one daily injection. When the dose of hGH was 32 or 8 micrograms per day, longitudinal bone growth and body weight gain were more pronounced in animals receiving the hormone 2 and 4 times per day compared with animals receiving the hormone one or 8 times per day. The results of the present study demonstrate that the frequency of GH administration influence body growth. The findings suggest that the secretory pattern of GH influence the growth rate under in vivo condition.