Aqueous extracts of corpus cardiacum from Periplaneta americana L. elicit the characteristic locust response of hyperlipemia when injected into adult male Locusta migratoria migratoides R. and F. Conversely, gland extracts of L. m. migratoides cause the typical cockroach response of hypolipemia when injected into adult male P. americana.It is proposed that similar factors are present in both species with specificity being determined at the site of action.