Two juvenile hormones are isolated from organ cultures of corpora allata of the tobacco hornworm moth, Manduca sexta Johannson, and are purified by high-resolution liquid chromatography. These are identified as methyl (2E, 6E)-(10R)-10,11-epoxy-3,7,11-trimethyl-2,6-dodecadienoate, a new natural hormone, and methyl (2E,6E) - (10R,11S) - 10,11 - epoxy - 3,7,11 - trimethyl-2,6-tridecadienoate. [(14)C]Methionine is incorporated only into their methoxycarbonyl group. Details of the in vitro techniques and the chemical proof of structures are presented. The significance of the occurrence of a new juvenile hormone and the new techniques used for production, isolation, and identification are discussed.