Diagnosis of arylcyclohexylamine intoxication is based on behavioral changes that occur following ingestion of phencyclidine: belligerence, assaultiveness, impulsiveness, unpredictability, psychomotor agitation, and impaired judgment. Low-dose intoxication (5–10 mg) results in agitation, excitement, catalepsy, or mutism ( Burns and Lerner 1976 ). With severe phencyclidine intoxication, patients are unresponsive and comatose, but their eyes remain open (Pearlson 1981). Although not discrete from one another, three stages for phencyclidine intoxication ( Rappolt et al. 1980 ) have been described, depending on the dose taken: the stage of behavioral toxicity, the stuporous stage, and the comatose stage (Table 16B–1). The patient may fluctuate between the stuporous stage and the behavioral toxicity stage over a 1- to 2-hour period. The comatose stage may last from 1 to 4 days, depending on the dose taken and the rate of excretion.