SUMMARYIntermediate-chain-length fatty acids (C8-C14) inhibit growth and respiration of fungi under conditions where the longer- and shorter-chain acids are noninhibitory. Under the conditions tested, lauric and capric acids (0.02 M,pH 5.5) inhibited endogenous O2uptake byCunninghamella echinulata.The inhibition was not permanent and the organism recovered when given sufficient time in contact with the substrate. Recovery from the inhibition was O2dependent, since cell preparations incubated under nitrogen failed to recover. Supplemental coenzyme-A stimulated the rate at which the organism recovered from the respiratory inhibition by capric and lauric acids. Furthermore, pantothenic acid reversed the inhibition by these acids, and hydroxylamine stimulated the rate of recovery from laurate inhibition. The rate of recovery was inversely related to the chain length of the acid at equimolar concentrations. The findings indicate that the mechanism by which these acids inhibit endogenous respiration is to be understood at the enzymic level. Moreover, the data presented show a definite involvement of coenzyme-A and its acyl derivatives in the mechanism by which the intermediate-chain-length acids inhibit endogenous respiration in this fungus.