1. The effects of frequency of orthodromic and antidromic stimulation of CA3 on formation of electrographic seizurelike discharges in CA1 was studied in the high potassium hippocampal slice. 2. Within the range of stimulation of CA3 used, 0.1-10.0 Hz, a narrow range was identified between 1.0 and 1.3 Hz, where the tonic phase of seizure generation in CA1 was suppressed. This suppression was observed for both Schaffer collateral and mossy fiber stimulation.