Isoflurane (1-chloro-2,2,2-trifluoroethyl difluoromethyl ether) is a potent general anesthetic agent that is highly adaptable to use in small laboratory animal species. Respiratory delivery is easily accomplished in these animals, even during restraint in a stereotaxic apparatus. The ease of administration, high predictability of action, and ability to finely control the depth of anesthesia make isoflurane anesthesia far superior to regimes involving injectable anesthetics. The wide margin of safety of isoflurane is a key indicator of the superiority of this product to all other anesthetic agents. The initial cost associated with the delivery system is a drawback, but the reliability and safety factors outweigh the hardware costs.