Biosynthesis with 14C-glutamic acid and 14C-glutamine in a hypothalamic system followed by fraction yielded fractions after defatting, Bio-Gel P2, CMC, and Sephadex G25 partition chromatography which released 40,000 to >128,000 ng/ml of FSH. The decapeptide, pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH 2 released about 18,000 and rarely up to 35,000 ng/ml of FSH. Radioactivity was associated with these exceptionally active FSH-fractions. The apparent new hypothalamic hormone releases both FSH and LH and can be FSHRH which is different from the decapeptide which is apparently LHRH and not LHRH FSHRH The associated radioactivity and FSH-releasing activity indicate that FSHRH may have a pGlu-moiety.