Amphenone 'B' treatment resulted in the hypertrophy and degranulation of the B3 cells of the pars distalis and stimulation of interrenal cells, whereas administration of dexamethasone caused regression of B3 and interrenal cells. Following 15-day cessation of amphenone or dexamethasone treatment, there was no recovery in the B3 or the interrenal cells. The results suggest that B3 cells are the probable source of ACTH and there exists a relationship between the pituitary and interrenal gland of the frog, R. cyanophlyctis.