Cell bodies immunoreactive for methionine- and leucine-enkephalin are found in the area of the locus coeruleus (dorsolateral pons) of the cat after injection of colchicine in the ascending projections of the nucleus. Using radioimmunoassay procedures, it is shown that colchicine induces a significant increase in methionine- and leucine-enkephalin-immunoreactive material in this area of the brain. High pressure liquid chromatography analysis demonstrated that the immunoreactive materials were authentic methionine- and leucine-enkephalin. The methionine- and leucine-enkephalin patterns were identical in the colchicine injected and non-injected sides of the dorsolateral pons. It is suggested that, in this area of the brain, colchicine (i) does not significantly modify the processing of proenkephalin to form the pentapeptides methionine- and leucine-enkephalin, and (ii) does not induce the appearance of new substances reactive to the enkephalin antisera employed.