It is postulated that some, if not all, anesthetic actions can be explained on the basis of interaction between anesthetics and hydrophobic areas of protein molecules in addition to their effects on membrane lipids. We have studied molecular perturbations using high resolution nuclear magnetic resonance techniques and changes of activity of enzymes and oxygen affinity of hemoglobin. Although the specific cellular and molecular mechanisms of anesthesia are unknown at present, useful information on the physical properties of the "drug receptor sites" can be inferred from interactions of anesthetics with pressure in intact animals. The present evidence indicates that different anesthetics have different specific molecular sites with only a limited degree of occupancy. These differences between agents at a molecular level of action are relevant both to the effects on the central nervous system and also to the many "side effects" of anesthetics.