During presurgical evaluation, bilateral intracarotid amobarbital tests were performed in 21 patients (42 tests) to establish the lateralization of cerebral speech dominance as well as memory function. All patients suffered from long-standing, medically intractable, complex partial seizures. Electrocorticographic recording during the investigation was carried out via bilaterally implanted subdural electrodes. The aim of the study was to assess amobarbital-induced effects on the primary epileptic focus, determined throughout presurgical evaluation. Following the application of amobarbital the primary epileptic focus was selectively activated in 10 and preferentially activated in 3 patients suffering from temporal lobe epilepsy. Specific responses of the primary epileptic focus consisted of: (i) induction of a spike-burst-suppression pattern, mainly in the mesio-basal aspects of the focal temporal lobe (n = 13); (ii) induction of spikes or sharp waves following contralateral intracarotid injection (n = 10); (iii) late induction of spikes or sharp waves following ipsilateral injection (n = 4); (iv) loss or marked reduction of drug-induced beta activity over the primary epileptic focus (n = 14) following ipsilateral or contralateral injection. In conclusion, electrocorticographic recording during the intracarotid amobarbital test contributes valuable information about the primary epileptic focus in a high proportion of patients.