The present study was performed to see if first-generation histamine H₁-antagonists are useful sedative-hypnotic drugs. Increases in electroencephalogram (EEG) power spectra of the delta band (0-4Hz) at the frontal cortex and theta band (4-8Hz) at the hippocampus in rats were used as an indexes of sleep. The H₁-antagonists used in this study resulted in a decrease in sleep latency and an increase in sleep duration (slow wave sleep). The rate of REM (rapid eye movement) sleep during slow wave sleep was decreased by H₁-antagonists and brotizolam. The order of potency of H₁-antagonists for the reduction in sleep latency (from greatest to least) was promethazine>chlorpheniramine>diphenhydramine and pyrilamine, and that for the increase in sleep duration was chlorpheniramine>promethazine>diphenhydramine and pyrilamine. Brotizolam was more potent than these H₁-antagonists, with 14-18-fold and 4-14-fold greater effects on sleep latency and duration, respectively. These results clearly show that H₁-antagonists are effective in mild to moderate insomnia as sedative-hypnotic drugs.