A multicenter, double-blind placebo-controlled clinical trial was designed to compare the safety and efficacy of estazolam compared with flurazepam as hypnotics. Outpatients complaining of insomnia were randomized to receive either estazolam 2 mg, flurazepam 30 mg or placebo for 7 consecutive nights. The analysis of efficacy was based on the patients' daily assessments of sleep and the investigators' global evaluations. Adverse events which were considered by the investigator to be attributable to, or of unknown relationship to the test medication were analyzed. The patient subjective questionnaire indicated that estazolam and flurazepam significantly improved all parameters (P less than .05) as compared to placebo. A marked or moderate improvement in sleep was reported by 81% (58/72), 78% (63/81) and 36% (27/76) of estazolam, flurazepam, and placebo recipients, respectively. There were no significant differences in hypnotic effect between estazolam and flurazepam. All efficacy parameters of the investigators' global evaluation improved significantly more (P less than .05) for patients receiving estazolam or flurazepam (except quality of sleep) than for those receiving placebo. The percentage of patients reporting any adverse experience was greatest for flurazepam (72%), followed by estazolam (59%), and placebo (43%). Somnolence and hypokinesia were the most commonly reported adverse events. An analysis of the global evaluation of side effects showed that flurazepam had a significantly worse side effect profile than estazolam (P less than .05) or placebo (P = .001). Estazolam and flurazepam effectively, and comparably, relieved insomnia when administered for 7 nights in adult patients complaining of insomnia. Estazolam demonstrated a more favorable side effect profile than flurazepam.