A single 10 mg dose of zolpidem, an imidazopyridine hypnotic, was administered to young, healthy male volunteers prior to bedtime. The drug reduced REM sleep but did not significantly affect other sleep stages and subjective sleep parameters. All-night spectral analysis of the EEG revealed that power density in nonREM sleep was reduced in the low-frequency range (1.25-2.5 Hz; 5.25-10.0 Hz) and increased in the spindle frequency range (12.25-13.0 Hz). Significant changes in the EEG spectrum were present in the first 4 h of sleep. The pattern of the spectral changes was similar to those induced by other hypnotics that bind to the GABAA/benzodiazepine receptor complex. There were no residual effects of zolpidem on psychomotor performance in the morning, on the self-rated state in the morning and at noon, and on sleep and EEG parameters in the subsequent drug-free night.