Abstract 1. Extraction by ether removes only about one-half of antimycin added to sub-mitochondrial particles, independently of the amount of antimycin added up to that necessary for 100% inhibition. 2. The amount of antimycin extractable with ether remains the same even when the antimycin is redistributed between an antimycin-inhibited preparation and an untreated. The antimycin remaining after ether extraction is redistributed between ether-accessible and ether-inaccessible sites when the preparation is incubated on its own or with an untreated preparation. 3. Low concentrations of cholate increase the extractability of the antimycin by ether. 4. Complex III binds antimycin more firmly than sub-mitochondrial particles. However, antimycin is readily extracted by ether, leading to restoration of enzymic activity and cleavage of the complex by bile salts. 5. The results are consistent with an explanation of the sigmoidal inhibition curve with antimycin and preparations of the intact respiratory chain in terms of an allosteric model.