The distribution in the sheep omasum of peptide- and catecholamine-containing neurons was investigated by an immunohistochemical technique using antibodies against six neuropeptides and two catecholamine-synthesizing enzymes. In the myenteric plexus, both nerve cell bodies and nerve fibers were positively immunostained for substance P (SP), methionine enkephalin (ENK), vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY) and galanin (GAL). In contrast, immunoreactivity specific for calcitonin gene-related peptide (CGRP), tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) was detected only in nerve fibers. In the omasal wall, nerve fibers with SP- and ENK-like immunoreactivity were prominent in the outer muscle layer, while numerous nerve fibers with VIP-, NPY- and GAL-like immunoreactivity were observed in the inner muscle layer. In the lamina propria mucosae, and in particular in the omasal papillae, a dense network of peptide-containing nerves was found. The distribution of nerves with CGRP-like immunoreactivity was different from that of other immunoreactive nerves. The networks of nerves with TH-, DBH- and NPY-like immunoreactivity were concentrated around the vascular components. The results of this study indicate the complexity of the enteric nervous system in the sheep omasum, reflecting the multiple functions of the nerves in the regulation of motility and/or absorption and secretion.