A transient insomnia model, the "first night" effect in the sleep laboratory, was used to assess the dose range for the hypnotic and sleep stage effects of temazepam. 201 healthy, normal subjects (97 men and 104 women), 21 to 49 years old, with no sleep complaints were studied. Each was randomly assigned to receive either placebo, 7.5, 15, or 30 mg temazepam hard gelatin capsules (Restoril) administered double-blind 30 min before bedtime on their first night in the sleep laboratory. Over the 8-h polysomnogram total sleep time and sleep efficiency increased significantly in a linear fashion with increasing doses of temazepam. Sleep tendency was significantly reduced by increasing doses again in a linear manner. Wake time during the sleep period was reduced significantly only by the higher dose. The percentage of stage 1 sleep was reduced and the percentage of stage 2 sleep was increased, each linearly with increasing doses. These data are the first to demonstrate the hypnotic effects of a 7.5 mg dose of temazepam and also support previous studies of 15 and 30 mg temazepam administered to chronic insomniacs. They also illustrate the utility of the "first night" effect as a model of transient insomnia.