AbstractTwo analogues of aManduca sextaallatotropin (Mas‐AT) were synthesized. They correspond to the active fragment, amino acids 5–13, of the natural Mas‐AT with substitution of norleucine for methionine. ATANA has the structure Val‐Glu‐Nle‐Nle‐Thr‐Ala‐Arg‐Gly‐Phe‐NH2, ATAA is acetylated at the N‐terminus. Allatotropic potency was evaluated by measuring the in vitro rates of juvenile hormone (JH) biosynthesis in corpora allata (CA) ofM. sexta.At a concentration of 20 nM, ATANA and ATAA increased JH production in day 0, day 1, and day 3 adult female CA by a factor of 3–8. Larval CA were not affected. These results correspond to activities reported for the natural Mas‐AT. ATANA did not stimulate pharate adult female CA to produce JH. Stimulation of female CA with ATANA was reversed when the CA were transferred to fresh medium while stimulation with ATAA under the same condition persisted.Exogenous farnesoate was converted to JH‐III at a rate exceeding the highest ATANA‐stimulated rate. ATANA in addition to farnesoate did not increase JH‐III production, but increased JH‐II production in addition to the already high production rate for JH‐III. It is inferred that Mas‐AT stimulates a rate‐limiting enzyme in the biosynthesis of farnesoate and its homologues but