Seven-hour sleep EEG recordings were obtained from rats (N = 15) given a single acute dose, and rats (N = 15) given 14 daily doses of zimelidine, 20 mg/kg IP. REM latency, REM sleep, number of REM episodes, and total sleep time were significantly affected by zimelidine administration when compared to controls, as well as to each animal's baseline sleep parameters. Sleep latency and slow-wave sleep were not significantly affected by zimelidine. The results are discussed in terms of the implications of the use of zimelidine as a clinical treatment for depression, as well as the implications for the use of REM changes as a diagnostic indicator of the efficacy of treatment with zimelidine.