Histochemical evidence is presented for a catecholamine-containing projection from the nucleus locus coeruleus to the neocortex in the squirrel monkey. The innervation of superior temporal gyrus has been examined in particular. Glyoxylic acid-induced fluorescence shows an extensive arborization of fine, catecholamine-containing fibers with prominent varicosities in all layers of the neocortex. The nucleus locus coeruleus is identified as a source of these fibers by both ortho- and retrograde axonal tracing techniques. After injection of horseradish peroxidase into the neocortex, labelled cell bodies are localized throughout the major portions of the locus coeruleus. Conversely, after microinjection into the nucleus locus coeruleus, tritiated proline is transported into the neocortex where it appears within fibers similar in distribution to those revealed by fluorescence histochemistry. Both transport techniques indicate that cortical projections of the locus coerculeus originate from both ipsilateral and contralateral nuclei.