In a retrospective study of the EEG sleep of major depressives with & without a history of suicide attempts, suicide attempters had longer sleep latency, lower sleep efficiency & fewer late-night delta wave counts than normal controls. Nonattempters, compared to attempters, had less REM time & activity in Period 2, but more delta wave counts in non-REM Period 4. Findings are discussed in the context of current theories on the role of serotonin in the regulation of sleep & in suicidal behaviour.