Rats were prepared with permanent electrodes for recording the electroencephalogram (EEG) and the electromyogram (EMG) and made morphine dependent by the subcutaneous implantation of morphine pellets. Abstinence was then precipitated by removal of the pellets 72 hours later. The evaluation of continuous EEG and EMG recordings revealed a maximal reduction in the amount of REM sleep and a decline in its EEG voltage output during the first day after pellet removal. Both the duration of REM sleep and its mean integrated EEG voltage returned to the baseline levels by the second day of abstinence. A significant but short-lived REM rebound subsequently followed and was accompanied by a trend toward elevation of the mean EEG voltage. These changes are reminiscent of similar findings in rats withdrawn from morphine administered intravenously (Khazan and Colasanti, 1971, 1972). The smaller magnitude of changes in rats treated with morphine pellets, however, may suggest a lower degree of drug dependence.