Intraperitoneal administration of 5-10 mg/kg of THIP (4,5,6,7 tetrahydroxyisoxazolo (4,5,c) pyridine 3-ol) induced a transient, reliable model of bilaterally synchronous spikes and waves in rats. The paroxysmal bursts elicited by THIP had similar topographical distribution to the spontaneously-occurring spike and wave discharges often observed in naive rats. The responsiveness to electrical stimulation of subcortical nuclei was different in the two models. Systemic administration of THIP provided a simple, reliable model of bilaterally synchronous spike and wave discharges that may involve the same cerebral structures as those involved in the generation of the spontaneous paroxysms. The administration of the drug increased the yield of paroxysmal responses and provided a stable and predictable 4 hr test situation that may easily be quantified.