1. Studies were made on the effect of reserpine on development and its neuro-endocrine regulation in Galleria mellonella. It was shown that resperine greatly restricts the development of this insect. 2. Reserpine causes inhibition of the activity of the neurosecretory cells of pars intercerebralis of the brain in the insects examined, measured by the degree of RNA synthesis in these cells. It also restricts the secretion of neurosecretion from these cells and consequently leads to its excessive accumulation. 3. Injection of reserpine causes an increase in the level of K+ and Na+ in the haemolymph of G. mellonella. 4. A discussion is given of the probable participation of ecdysone in regulation of the level of sodium and potassium ions in the haemolymph of G. mellonella.