Sleep patterns were recorded during 5 weeks of chronic treatment with sodium barbital and after abrupt cessation of drug administration. Sodium barbital was administered intragastrically to adult cats twice daily in doses to produce a peak response of gross ataxia (“low-dose” barbiturate treatment). Sleep stages were scored from EEG, EOG, and neck EMG recordings from chronically implanted electrodes. Sleep was monitored continuously for 48 h once each week during barbital administration and continuously for 7 to lO days during withdrawal. Rapid eye movement (REM) sleep during barbital treatment was reduced to approximately half compared with control. At the end of the treatment, equivalent doses of pentobarbital were substituted for barbital. Cessation of pentobarbital administration produced withdrawal. Withdrawal intensity was moderate and spontaneous convulsions occurred in half the animals. The duration of withdrawal insumnia was 2 to 3 days. Return of the non-REM and REM sleep was associated with changes in withdrawal behaviors, notably the appearance of overly affectionate behavior. Furthermore, during return of sleep both non-REM and REM sleep increased to values greater than control.