Intracarotid injections of amobarbital have been performed for clinical purposes since 1949, when Wada described a method for determination of hemispheric language dominance. It was noted that the intracarotid injection of amobarbital, performed in an attempt to investigate the interhemispheric spread of epileptiform discharges, produced a transient ipsilateral paralysis of hemispheric function without eliciting unacceptable sedation or interruption of vital functions. It was reasoned that this method would be useful for determination of hemispheric language dominance in patients who were to undergo neurosurgical procedures on the language dominant hemisphere (Wada, 1949). Eighty patients were evaluated by Wada between 1948 and 1954 without major complications (Wada and Rasmussen, 1960).