Deuterium is selectively incorporated into the ring positions of-l-methylnaphthalene from gaseous deuterium, and the distribution of deuterium in the rings is essentially the same in the presence or absence of coal. Incorporation is under kinetic control. Ring exchange appears to be due to catalysis by the walls of the reactor. Incorporation in the methyl position does not occur to an appreciable extent at 385 or 450 degrees C in the absence of coal, but extensive incorporation does occur in the presence of coal. The pattern of ring substitution of deuterium precludes, or places severe restrictions on, the role of hydrogen shuttling by l-methylnaphthalene as an explanation for the observation of higher coal conversion in this nondonor solvent than in a donor solvent, tetralin.