A chimeric recombinant human gonadotropin, termed C3, demonstrates both follitropic and lutropic bioactivities. The alpha subunit construct for C3 is comprised of the recombinant wild-type human glycoprotein hormone alpha subunit (). The subunit DNA construct for C3 encodes residues 1-145 from human chorionic gonadotropin (hCG) beta () with the exceptions that FSH amino acid 88 (D) is substituted for hCG amino acid 94 (R) and FSH amino acids 95-108 (TVRGLGPSYCSFGE) are substituted for hCG amino acids 101-114 (GGPKDHPLTCDDPR). C3 is a potent FSH and LH agonist able to bind and to signal through FSH and LH receptors in vitro. In in vivo bioassays optimized to quantify each type of activity, C3 was found to have lutropin and follitropin potencies at levels similar to those of rhLH and rhFSH, respectively. In immature rats, C3 was sufficient to support the maturation of normal ovarian follicles. Moreover, a significant portion of follicles matured by C3 ruptured in response to an ovulatory hCG stimulus and gave rise to morphologically normal oocytes. Furthermore, a low dose of C3 promoted weight gain in the rodent uterus suggesting it also supported preparation for implantation without histological evidence of excessive luteinization of the ovary. In summary, the biological properties of C3 indicate that its chimeric nature has resulted in a fully functional, dual acting human gonadotropin.