This study was performed to investigate the effect of different cholinomimetic drugs (CD) on ACTH levels in betamethasone (BET) pretreated rats (40 mg/kg in the drinking water for 24 h). Animals were injected with atropine methylbromide (1 mg/kg, i.p.) and, after 10 min, with physostigmine (25, 50, 100, 200 micrograms/kg), arecoline (AR) or oxotremorine (OX) (150, 300 micrograms/kg) intravenously. They were killed 10 and 20 min after CD injection, to measure ACTH plasma levels. The lowest dose of AR and both doses of OX were able to induce an escape from BET suppression. The hypothesis that a stimulation of central muscarinic (and, probably, not nicotinic) receptors is involved in the CD-induced escape from glucocorticoid suppression is discussed.