Muscular atonia and cortical desynchronization, two signs of desynchronized sleep, can be enhanced or suppressed by direct injection of carbachol into the pontine brain stem of cats. The positive effects are graded, being maximal in the gigantocellular tegmental field and less marked in adjacent nuclei. These positive effects are dose-dependent. Suppressive effects of carbachol are maximal in the region of the locus coeruleus and are dose-dependent but do not exceed those of the vehicle alone. The results support the hypothesis that cholinergic mechanisms of the pontine tegmentum are involved in desynchronized sleep generation.