Intravenous (i.v.) methohexital (MTH, Brevital) was found to have an effect on the intraoperative electrocorticogram (ECOG) of 63 patients who had temporal lobectomies performed under general anesthesia for intractable complex partial seizures. In the preresection ECOG, MTH increased the frequency of spikes in 78%, the area of cortical spiking in 30% and induced seemingly "new" spike foci in 43%. Similar although less dramatic changes occurred in the final (i.e., postresection) ECOG. Whether these changes induced by MTH, specifically the new spike foci, are significant was assessed by correlating surgical results with the presence of "residual spikes" (i.e., after all resections, not spontaneously occurring but activated by MTH). Surprisingly, nine patients with residual "MTH-spikes" did not have any postoperative seizures whereas two had some. This raises the question of whether MTH effects are significant overall. Caution is advised in the use of MTH in intraoperative assessment of interictal spike fields, especially when new spike foci are activated. Further study of the possibility of false activation, with a larger series, is advised.