After the sc administration of 1, 10, and 50 µg of the LRF agonist [D-Trp6,Pro,9,NEt]LRF, dose-dependent increments in circulating levels of LH, FSH, and estradiol were observed which were 2- to 3-fold greater in the late than in the early follicular phase. The 10-μg dose of LRF agonist appears to induce a maximal acute gonadotropin-estradiol response. Both 10- and 50-μdoses of the agonist elicited gonadotropin increments which were several times greater than that seen during the midcycle surge. The only difference between the two doses was the more sustained action on gonadotropin release of the latter. It is estimated that this superactive LRF agonist is approximately 140 times more potent than the decapeptide LRF. These observations provide information useful in the application of this LRF agonist for clinical studies. (J Clin Endocrinol Metab50: 179, 1980)