Although sleep deprivation is known to exert an antidepressant effect in depressed patients, the involvement of sleep regulation is still unknown. Selective sleep deprivation experiments were performed in the rat to investigate the interactions between non-REM sleep (NREMS) and REM sleep (REMS) in an animal model. A12-h total sleep deprivation (TD) period ending at lights on was followed by one of the following protocols: (1) recovery sleep (TD12); (2) 4-h total sleep deprivation (TD16); (3) 4-h slow-wave deprivation (SWD); (4) 4-h REMS deprivation (RD). In the SWD protocol, the reduction of EEG slow-wave activity (SWA; power density in the 0.75-4.0 Hz band) was obtained by curtailing NREMS episodes to 20 s. During RD the number of interventions required to prevent REMS increased during the first 2 h and then remained constant. While RD caused only a minor reduction of NREMS, it increasingly suppressed SWA in NREMS. The rebound of SWA occurred later and was less prominent after RD than after SWD. Whereas an REMS rebound occurred after all three 4-h sleep deprivation protocols, a persistent increase in the dark period was present only after TD16. It is concluded that (a) SWA in NREMS is inhibited by an increased level of REMS propensity; (b) the hypothesis that REMS propensity increases only during NREMS is not supported; and (c) the results are compatible with the hypothesis that the suppression of NREMS intensity is the common denominator of different antidepressive sleep manipulations in depressive patients.