The influence of Lendormine (diazepine derivative) both on the sleep structure and subjective estimation of sleep was examined in 25 patients at the age of 19-64 years old with neurotic insomnia. The investigation was performed before, during and after 10 days of treatment (0.25 mg before the sleep time). The drug administration resulted in significant improvement of sleep structure that is in sleep duration and efficiency because the drug either promoted falling asleep or increased the second and the forth stages of sleep. Lendormine decreased also the wakening time inside the sleep. The polysomnographic results coincided completely with subjective estimation of sleep by patients themselves after the treatment. The optimal time of therapy didn't exceed 2 weeks. The drug was well tolerated without any complications. The conclusion is made about high effectiveness of Lendormine in the treatment of patients with insomnia.