Median nerve somatosensory evoked potentiais (SSEPs) were recorded in 21 healthy subjects anesthetized with halothane, isoflurane, or enflurance (with and without nitrous oxide) for abdominal or pelvic surgery. Recordings were made prior to induction, then at 0.5 MAC increaments of each valatile agent with 60% N2O up to 1.5 MAC, and, finally, at 1.5 MAC without N2O. All three volatile anesthetics produced dose-related reductions in the amplitude and increases in the latency of he cortical component of hte SSEP. These changes were most pronounced with enflurance nad least with halothane. At 1.5 MAC of each volatile agent, cortical latency decrease and amplutede increased when nitrous oxide was discontinued. The results suggests that in neurologically intact patients, end-tidal concentrations of 1. MAC halothane and 0.5 MAC enflurance or isoflurance (each in 60% N2O) can be compatible with effective with effective SSEP monitoring. Volatile anesthetic concentrations consistent with satisfactory somatosensory-evoked potential recording may be grater if N2O is not employed.