Specific agonists for muscarinic receptor subtypes were infused by microinjection into the medial pontine reticular formation of freely moving cats. The M2 agonists Oxotremorine-M and Cisdioxolane significantly increased REM sleep percentage. The results obtained with microinfusions of carbachol, a mixed muscarinic agonist, were similar to that obtained by the M2 agonists. The M1 agonist McN-A-343 did not elicit any change in sleep or REM sleep percentage. The generation of REM sleep by cholinergic stimulation of the medial pontine reticular formation may be mediated by the M2 muscarinic receptor subtype.