Evaluation of neuronal responses to single-pulse electrical stimulation (SPES) was performed to determine the reliability of cortical stimulation under general anaesthesia compared to alert awareness. Nine patients with intractable epilepsy, candidates for epilepsy surgery, underwent SPES during both electrode implantation and telemetry recording. Early, delayed, repeated, fixed and oscillatory neuronal responses to SPES were investigated. Analysis showed that: a) early responses are normal markers of synaptic efficacy, b) delayed responses are markers of epileptogenicity, c) repeated responses are normal variants of deep cortical stimulation, d) fixed responses are markers of normal connectivity underlying sensory processing functions, and e) oscillatory responses are normal markers of pacemaking capability of deep brain structures. This study produced evidence that the main pathological markers have a high correlation between implantation and telemetry SPES procedures. Results render SPES an equally reliable process under both anaesthesia and alert awareness.