Brown-adipose-tissue mitochondria isolated from golden hamsters were found to contain more CoA per mg protein than rat brown-fat mitochondria, and after incubation with erucoyl-carnitine, a higher free CoA level remained, than in rat mitochondria. In accordance with the suggestion (Alexson et al. (1985) Biochim. biophys. Acta 834, 149-158) that the inhibitory effect of erucoyl-carnitine on brown-fat mitochondrial respiration is entirely due to CoA sequestration, hamster mitochondria (with more CoA) were less sensitive to erucoyl inhibition than were rat mitochondria. Thus, increased mitochondrial CoA levels may augment the ability of animals to withstand the detrimental effects of a high erucoyl ester content of the diet.