The anaesthetic isoeugenol has been used as metabolic suppressant for commercial transport of live lobsters in order to decrease energy expenditure and improve survival. Given the central role of mitochondria in metabolism and structural similarities of isoeugenol to the mitochondrial electron carrier coenzyme Q, we explored the influence on mitochondrial function of isoeugenol. Mitochondrial function was measured using high-resolution respirometry and saponin-permeabilised heart fibres from the Australasian red spiny lobster, Jasus edwardsii. Relative to vehicle (polysorbate), isoeugenol inhibited respiration supported by complex I (CI) and cytochrome c oxidase (CCO). While complex II (CII), which also reduces coenzyme Q, was largely unaffected by isoeugenol, respiration supported by CII when uncoupled was depressed. Titration of isoeugenol indicates that respiration through CI has a half-maximal inhibitory concentration (IC50) of 2.4±0.1 µmol l−1, and a full-maximal inhibitory concentration (IC100) of approximately 6.3 µmol l−1. These concentrations are consistent with those used for transport and euthanasia of J. edwardsii and indicate that CI is a possible target of isoeugenol, like many other anaesthetics with quinone-like structures.