A procedure for implanting cortical and subcortical brain electrodes in young hooded rats is described. In unrestrained rats, cortical activity showed patterns of high voltage slow activity or low voltage fast activity correlated with quiet or alert states, respectively. Typical recruiting responses were elicited by stimulation of the mediodorsal thalamic nucleus. Low intensity stimulation of the limbic system produced an electrical response similar to thalamocortical recruiting, and higher intensity stimulation induced a seizure discharge in the limbic circuit with accompanying behavioral signs of excitement and hypermotility. Neither ongoing electrical activity, nor thresholds or amplitudes of response to stimulation of thalamus or limbic system were observably different after a period of 8 weeks of active growth of the rats.