Chemical analyses of wheat stem rust uredospores before and after germination indicated that the lipid fraction was the major endogenous substrate used up during the germination. Some nitrogenous material, presumably protein, was also utilized and increase in chitin was observed during the germination. A number of commercially available metabolic intermediary compounds did not affect the respiration of germinated spores. Heavy metal enzyme inhibitors, such as cyanide and azide, strongly retarded the respiration of spores and of germinated spores. This, together with the findings that the spore material contained hematin and reacted positively to the Nadi reagent, suggested that a cytochrome system was operative in the respiration process. Compounds such as malonate, maleate, fluoride, and fluoroacetate, known to be the inhibitors of succinic dehydrogenase and related enzymes, did not show significant inhibition of the respiration of rust spores. However, pyrophosphate, another specific succinic acid dehydrogenase inhibitor, retarded carbon dioxide production. Other inhibitors, such as iodoacetate, benzoate, and arsenate, inhibited respiration appreciably.