Sleep spindles and spike wave discharges are thought to originate from the same thalamic pacemaker. In the present work it is investigated whether sleep spindles and spike wave discharges are also sensitive for the same drugs. Adult male WAG/Rij rats were chronically implanted with frontal and occipital EEG electrode pairs. Rats were intraperitoneally injected with clonidine (0.00625 mg/kg), phenobarbital (20 mg/kg), flunitrazepam (0.188 mg/kg). Frontal and occipital sleep spindles and mainly frontal spike wave discharges were seen in the electroencephalogram. Phenobarbital and flunitrazepam reduced the number of spike wave discharges and enhanced frontal sleep spindles, while clonidine facilitated spike wave discharges and reduced frontal sleep spindles. The results of these three drugs indicate a reciprocal relationship between the number of frontal sleep spindles and the number of spike wave discharges. Only clonidine facilitated occipital sleep spindles without an effect on spike wave discharges. It can be concluded that frontal and occipital sleep spindles have a different pharmacological profile. Futhermore, the inverse relationship between frontal sleep spindles and spike wave discharges may suggest that sleep spindles and spike wave discharges are controlled by a single controlling system. However, in order to explain the clonidine data on occipital sleep spindles another factor must be incorporated in properties of the mechanism(s) involved in EEG oscillations.