Analytic electroencephalographic (EEG) sleep procedures were used to examine specific changes in rapid eye movement (REM) and slow wave sleep (SWS) as they unfolded during depressive illness and recovery. The subjects were 15 patients with recurrent depression who remained well during 3 years of nonpharmacologic maintenance treatment without a recurrent episode of major depression. The analyses were performed on EEG sleep studies conducted before acute treatment, after 3 months in maintenance treatment, and every 3 months thereafter for 3 full years of maintenance treatment. There was no change between the index sleep and sleep during the first year of maintenance treatment as determined by period analysis or visual inspection of REM sleep parameters, except that average REM counts decreased over time. Thus, it is possible that REM parameters may represent one indicator of long-term recovery from depression. Finally, a significantly higher amount of 12-20 Hz spectral power density was found during the index episode than during the period of remission.