The direct retorting of zinc sulfide concentrates in the presence of lime and carbon was examined on a laboratory scale in an apparatus that permitted the volatilized zinc to be condensed and weighed while the reaction gases were analyzed periodically with a gas chromatograph. The zinc vapor was calibrated on prepared gas mixtures of CO and cos and of co2 and so2 in nitrogen. Neither of these sulfur gases were detected. Going from 90% to 110% of theoretical reagents and from 1,100 deg to 1,200 deg c increased recovery of zinc from 75% to 93%. It was found that above 600 deg c, where carbon gases were first detected, reaction proceeded almost twice as fast for oxide plus carbon as for sulfide plus lime and carbon. Since cas might react with the atmosphere to give off sulfur gases, it was attempted to stabilize it by oxidizing to caso4. Because a residue of zns remained in the material from incomplete retorting, so2 was evolved while the cas oxidized. Oxidation was 20% complete at 800 deg c, rising to 90% at 1,200 deg c. It was concluded that while the retorting step is nonpolluting, if stabilization of cas is included in the process, the pollution is a problem.