Patients with primary insomnia typically complain of daytime fatigue and stress and have been shown to have long latencies on the Multiple Sleep Latency Test and increased whole body metabolism. However, typical treatment strategies for patients with insomnia rarely include any component to deal with these daytime symptoms. In the present study it was hypothesized that a 24-h treatment, lorazepam 0.5 mg TID, would be superior to an evening treatment, lorazepam 1.5 mg HS, in patients with primary insomnia. In a repeated measures crossover design, 12 patients with chronic insomnia received placebo or lorazepam 0.5 mg TID in one 4-night lab stay and placebo or lorazepam 1.5 mg HS in another lab stay. Both doses of medication were effective in improving objective and subjective measures of sleep and in reducing nocturnal whole body metabolic rate. Latencies on daytime nap testing were significantly reduced from a 14-min average to an average of 10 and 12 min, respectively, in the lorazepam 0.5 and 1.5 mg conditions. Significant differences were not found on psychomotor performance. Subjective reports of anxiety and confusion were increased in the morning after receiving lorazepam 0.5 mg in the evening but tension was reduced and subjective alertness was improved in the evening after daytime administration of lorazepam 0.5 mg. It was concluded that measurement and treatment of daytime symptoms is appropriate in patients with chronic insomnia but that rebounds in anxiety near the end of metabolic activity of lorazepam may make it a poor treatment choice. Int Clin Psychopharmacol 14:81-89 (C) 1999 Lippincott Williams & Wilkins.