The effects of delta sleep inducing peptide on metaphit (1-[1(3- isothiocyanatophenyl)-cyclohexyl] piperidine) provoked seizures in adult rats depending on whether it was administered prior or upon metaphit were studied. Animals were administered: 1. saline; 2. metaphit 3. DSIP and 30 min later metaphit (protected group); 4. metaphit and 8 h later DSIP (blocked group) or 5. DSIP alone. Upon the treatment, the rats were exposed to sound stimulation at hourly intervals and the incidence and behavioral severity (running, clonus and tonus) and EEG correlates of seizures were analyzed . Metaphit produced EEG abnormalities as spikes and spike-wave complexes and increased power spectra. Time-course studies revealed the peak of convulsive activity 7-12 h after metaphit administration. DSIP significantly increased power spectra of _ band no matter whether it was injected prior or after metaphit. Treatment with DSIP prolonged latency and reduced all convulsive components for a long period, as well as the mean seizure grade, but it was more pronounced in the protected than in the blocked group.