The most common method of separating autonomic nervous system and striate muscular response components of behavioral acts has been the use of pharmacological blockade of the skeletal response system, usually through the use of d-tubocurarine. The implication in studies using curare is that the major, if not only, change produced in the organisms by curare or curare-like drugs is muscular blockade. However, the mixed results obtained in both operant and classical conditioning of curarized organisms have led to this basic assumption being questioned. To the extent that curarization alters the physiology of the organism, other than by simply preventing nerve impulses from reaching the muscle, then to that extent the usefulness of curare as a tool may be compromised. The problems in using curare may be segregated into two classifications: (a) those problems directly associated with producing and maintaining a paralyzed organism including the criteria of muscular blockade and artificial respiration; and (b) those problems associated with the side effects produced by the drugs including ganglionic blockade, promotion of histamine release, and alteration of sensory processes.