Previous work suggested that the presence of an anti-diuretic hormone, particularly in the control of Malpighian tube function, was unlikely in Schistocerca gregaria (Mordue, 1969; Mordue & Goldsworthy, 1969). However, in Locusta migratoria it is claimed that both diuretic and anti-diuretic hormones regulate water balance (Cazal & Girardie, 1968). The experiments described here analyse the reciprocal effects of hormones from the pars intercerebralis—corpus cardiacum neurosecretory complex in both S. gregaria and L. migratoria upon the Malpighian tubes and rectum. It is necessary to separate the corpus cardiacum into its different lobes since the gland is known to function as an endocrine organ per se, as well as storing cerebral neurosecretion. The effect of hormonal extracts upon rectal and Malpighian tube function was studied by methods described previously (Mordue, 1969; Mordue & Goldsworthy, 1969). The increase in the rate of excretion through the Malpighian tubes of locusts caused by extracts of