ABSTRACT.Incubation of corpora allata (CA) from adult females ofLocusta migratoria(L.)in vitroin medium with a potassium concentration of 50 mM results in an elevation of the rate of juvenile hormone (JH) release. This elevation is however delayed, becoming apparent after the glands have been returned to low concentration of potassium but it is also prolonged, lasting up to 270 min. The elevation is initially modest but becomes more marked with time. The response of glands to high concentration of potassium is heterogeneous and appears to some extent to be a function of the initial rate of JH release of the glands. Glands starting with low rates of JH release are stimulated strongly by potassium, those with high rates of JH release much less so. Co‐incubation of glands with high concentration of potassium and with calcium channel blockers (both organic and ionic) prevents the elevation of release rates otherwise consequent on high concentrations of potassiu