Nine depressed inpatients slept from ten to 32 nights in the lab. Night-by-night fluctuations in their EEG sleep recordings were correlated with daily changes in Beck depression scores. A "percentage of phasic REM" measurement was obtained nightly by computing the percentage of 30-second epochs during REM containing at least one eye movement. Nightly fluctuations in percent phasic REM were inversely related to day-by-day changes in depression. This relationship was found whether a patient was treated with ECT or antidepressants. The results suggest that depression might be related to the malfunctioning of a pontine sero serotenergic gating mechanism for the control of PGO spiking during the REM.