Sleep loss and increased sleepiness on the job are among the most prevalent problems encountered by people involved in night shift work, especially in cases of abrupt shift of the wake-sleep cycle. In such conditions, detrimental effects on performance are well documented. In these situations, to avoid decrements of performance at night, one possibility is to use hypnotics for improving the quality and quantity of daytime sleep. In this study, we evaluated the effects of 20 mg of temazepam on daytime sleep, the subsequent levels of nocturnal alertness/sleepiness, and performance in a laboratory simulation of acute night shift. For evaluating alertness, sleepiness, and performance we used, respectively, the maintenance of wakefulness test (MWT), the multiple sleep latency test (MSLT), and two pencil and paper tests: digit symbol substitution test (DSST) and deux barrages test (DBT). All tests were administered four times at 2-hour intervals during the nighttime after daytime sleep. Results showed that the ability to maintain wakefulness (MWT) and to perform some visuo-attentive tasks were substantially maintained during the night. On the other hand, sleep tendency (MSLT) linearly increased during the night. Temazepam resulted in being an effective diurnal hypnotic, increasing total sleep time with no residual detrimental effects on sleepiness and performance and with an increase in the ability to stay awake.