MAC determinations for halothane, enflurane, and isoflurane were performed in New Zealand white rabbits (n = 8, approximate age 6 months). The MAC values (±SD) were as follows: halothane 1.39 · 0.23%, enflurane 2.86 · 0.18%, and isoflurane 2.05 · 0.18%. Comparison of these results with published MAC values for other species suggests that the ratio of the potencies for any pairing of these three agents is constant from species to species. This observation provides a means for assessing the validity of preexisting or newly determined MAC values.