Neither hydrogen sulfide nor any other volatile sulfur metabolites were found in the expired breath of mice given sodium sulfide intraperitoneally in doses up to the LD50. The detection system was sensitive to less than 0.1% of the sulfur in the given dose. The intraperitoneal administration of dimethyl disulfide resulted in its appearance in the expired breath of mice as well as much smaller amounts of both methanethiol and dimethyl sulfide. The intraperitoneal administration of methanethiol resulted in its pulmonary excretion as well as that of dimethyl sulfide. Administration of dimethyl sulfide led to its appearance alone in expired breath. Mice pretreated with ammonium acetate and then injected with dimethyl disulfide excreted the same three compounds via the lungs as above, but there were complex changes in the proportions and in the time sequence of their appearance. The absolute amounts of all three were increased, and the peak excretion for each was delayed. The amount excreted as dimethyl sulfide was particularly increased.