Minimal anesthetic requirements for cyclopropane, nitrous oxide, thiopental, ether, halothane, and methoxyflurane in the toad were studied. Requirements in the toad at room temperature were similar to those in the dog and in man at body temperature. The effect of temperature on halothane requirements in the toad was comparable to the effects of temperature in the goldfish and the dog. When halothane and methoxyflurane were carried in 100 per cent oxygen anesthetic requirements were higher than with 20 per cent oxygen. It made no difference whether nitrogen or helium was the third gas. Reserpinization of the toads abolished this effect of oxygen on anesthetic requirements, decreased anesthetic requirements, and reduced catecholamine concentrations in myocardium and brain.