Ten=hour sleep monitoring was carried out in 34 patients suffering from a vital depressive illness as well as in a group of 16 healthy volunteers; 18 of the depressed patients were deprived of treatment. The EEG was evaluated visually for data concerning the REM cycle and the REM latency. Spectral analysis of the all-night recordings yielded interval histograms for a group comparison of background activity. Fourier spectrograms and digital filtering were used to analyze ultradian patterns within the long-term frequency distribution. The result showed a trend in depression toward prolongation of the REM cycle and shortening of REM latencies. More significant, however, was the activation of 16- to 8-Hz waves together with a decreased occurrence of delta activity in depressed subjects without treatment. Depressed patients had significantly slower ultradian periodicities with 102-min cycles compared to 86-min cycles in healthy subjects. This disturbance could be temporally located in the early morning hours.