Supine and sitting lower extremity cortical somatosensory evoked potential (CSEP) examinations were performed in 30 healthy volunteers to establish normal values and to determine variations in SEP parameters caused by positional changes, side of stimulation, and the influence of height. CSEPs were recorded at Cz'-Fz (10-20 international EEG system) after stimulation of the saphenous, peroneal, and sural nerves at the ankle. Each nerve was tested in the supine and sitting positions. CSEP P1, N1 latencies and P1 - N1 amplitudes were recorded. The mean values of these parameters and side-to-side differences were determined for both positions. Parameter changes between the two positions were also determined. No statistically significant difference was found when comparing supine and sitting, or side-to-side values (p greater than 0.05). Regression analyses of P1 latency vs height revealed a significant positive correlation for both positions (p less than 0.0001-0.0045). Mean P1 and N1 latencies (msec) +/- 1SD, and mean P1 - N1 amplitudes (microV) +/- 1SD are as follows: peroneal nerve (n = 119) P1 = 39.5 +/- 2.98, N1 = 48.2 +/- 3.79, P1 - N1 = 1.41 +/- 0.81; sural nerve (n = 119) P1 = 41.3 +/- 4.03, N1 = 50.9 +/- 4.57, P1 - N1 = 1.31 +/- 0.61; saphenous nerve (n = 119) P1 = 41.5 +/- 4.02, N1 = 50.4 +/- 4.10, P1 - N1 = 0.87 +/- 0.30. The normative data generated by this study will help clinicians to distinguish normal variations in lower extremity CSEP parameters.(ABSTRACT TRUNCATED AT 250 WORDS)