The reactivity of hydrogen in tetralin and in Taiheiyo coal in the presence of iron catalysts (pyrrhotite and iron pentacarbonyl (Fe(CO)(5))) and sulfur were investigated using tritium and S-35 tracer methods under liquefaction conditions. Coal liquefaction was performed for 30 min at an initial pressure of 5.9 MPa and a temperature of 400 degrees C in the presence of tetralin solvent and tritiated hydrogen, with and without a catalyst and S-35-labeled sulfur. The rate of coal conversion and the tritium distribution in coal were higher when Fe(CO)(5) and sulfur were used than were obtained with conventional pyrrhotite. Further, the coal products obtained with the use of Fe(CO)(5) and sulfur were lighter than those produced in the presence of added pyrrhotite. The results suggest that the catalyst derived from Fe(CO)(5) and sulfur was successfully dispersed in the coal and directly acted on the coal to increase both the rate of coal conversion and the tritium transfer from the gas phase to the coal. The iron catalysts greatly promoted the hydrogen exchange between the gas phase and the tetralin solvent in the absence of coal. Part of the added sulfur participated in the sulfur exchange reaction with the pyrrhotite catalyst. The addition of sulfur increased the amount of hydrogen incorporated into the coal. This suggests that sulfur promoted the formation of tetralyl radicals during the hydrogen transfer from the solvent to the coal.