A large dose of intravenous methamphetamine hydrochloride reproduced the amphetamine psychosis in 12 of 14 patients dependent on amphetamine sulfate and failed to produce a psychosis in two patients who were eventually found to have not used amphetamine regularly above the therapeutic dose range. The psychosis was the facsimile of the disorder observed during drug abuse鈥攁 schizophrenic-like state of paranoia in a setting of clear consciousness accompanied by auditory or visual hallucinations, or both, but without thought disorder. Since in some cases the onset of the psychosis was sudden and occurred within one hour of commencing the intravenous injection, hypotheses about depletion of catecholamines and long term metabolites may need to be reconsidered.