AbstractThe nucleus locus coeruleus of the cat brain was studied using the Falck‐Hillarp fluorescent histochemical method for the demonstration of cellular monoamines. In the cat, as in other mammals, the locus coeruleus is made up of catecholamine‐containing neurons. The cell bodies of these neurons are diffusely distributed in the dorsolateral pontine tegmentum, occupying a portion of the lateral central gray and extending laterally across the paralemniscal tegmental field to surround the brachium conjunctivum in its marginal nucleus. The neurons of the locus coeruleus are readily distinguished from others in the area in Nissl‐stained material as well as in that prepared by the Falck‐Hillarp method. No subdivisions of the nucleus are evident in either Falck‐Hillarp or Nissl stained material. The locus coeruleus nucleus appears to include those neurons previously identified as the magnocellular component of the marginal nucleus of the brachium conjunctivum and the Kölliker‐Fuse nucleus.