This chapter discusses effect of inhibitors on the respiratory chain, where the two inhibitors examined are antimycin A and cyanide. Many compounds are known to inhibit electron flow in the respiratory chain and the sites at which they act can be identified by examining the effect of these inhibitors on respiration induced by the substrate. Cyanide inhibits cytochrome oxidase at the end of the respiratory chain. Antimycin A blocks electron flow at the cytochrome b or cytochrome c step. Antimycin A and cyanide are highly toxic and must be treated with extreme care. Record the changes in mitochondrial respiration induced by antimycin A and cyanide inhibitors.