Effects of subanesthetic doses of ketamine (0.25 and 0.5 mg/kg) on memory, cognition, psychomotor function, subjective moods, and incidence of adverse reactions were investigated in 34 healthy young volunteers. The drug caused impairment of immediate and delayed recall. Most of the impairment was due to interference with retrieval processes. Recovery was virtually complete 60 minutes after administration. The incidence of adverse reactions was high. Benzodiazepines need to be administered even when ketamine is used in subanesthetic doses.