Five patients with clinical and EEG primary generalized or multifocal uncontrollable seizures underwent stereotaxic implantation of electrodes in both centromedian thalamic nuclei (CM). Each electrode consisted of a semiflexible array of three platinum-iridium wires, isolated except at their tips, which were separated by 4 mm. Bipolar, biphasic rectangular pulses were delivered in trains of 1 min every 5 min, alternating right and left side for sessions 2 h/day. Patients were followed for 3 months with charting of clinical seizures, daily 4-h EEG recordings from scalp and depth for 5 days and weekly thereafter. Baseline and 3-month evaluation of psychological performance through selected Beta R, Wechsler memory scale, visual discrimination, MMPI, and Zung's rated depression scale. Tests were evaluated for significant changes by the parametric student's t test and Mann Whitney nonparametric test. Clinical seizures were significantly reduced by electrical stimulation (ES), as were EEG interictal spikes and EEG slow waves. Psychological performance improved beyond that expected by reduction in seizure activity. ESCM induced a local afterdischarge (AD) that progressively developed in time and intensity, and the beneficial effects outlasted ES for periods of weeks to months, suggesting that a state of hyperexcitability of stimulated tissue, similar to "kindling," was created by chronic ES.