A study was carried out in 80 mild to moderately depressed patients seen in general practice to assess the relative effectiveness and tolerance of a single night-time dose compared with the usual divided daily dosage regimen of a chlordiazepoxide (5 mg)/amitriptyline (12.5 mg) combination. Patients were assigned at random to receive either 1 capsule 3-times daily or 3 capsules as a single dose at night over a period of 3 weeks. Self-assessments of anxiety and depression using the Leeds scale were made at the initial visit and at weekly intervals, and an assessment of overall response to treatment was made by the doctor at the end of the trial period. Both groups showed significant improvement at each visit but the results suggest that the single night-time dose was more effective than the same dose given in a divided regimen. The good response obtained on relatively low doses of the tricyclic would support the view that chlordiazepoxide potentiates the antidepressant effects of amitriptyline.