First night effect in depression: new data and a new approach.

Polysomnography was performed in 20 depressed patients and 8 normal controls for 2 consecutive nights. A subset of patients had 3 consecutive nights. Patients were assigned to groups according to the presence (group I) or absence (group II) of a first night effect (REM sleep latency on the first night in the laboratory was at least 30 min longer than on the second night).