This prospective study meets all six criteria recently recommended by a quality assurance committee of the AAEM and defines criteria of abnormality, sensitivity and specificity of 19 sensorimotor and sympathetic parameters in 100 patients who were suspected on clinical grounds of having carpal tunnel syndrome (CTS), and in 70 control subjects. Nine parameters reached a specificity of 97%, permitting the electrodiagnosis of CTS in 87% of the patients studied. The results in this study confirm that median sensory nerve conduction studies are more frequently abnormal than are studies of motor nerve conduction. The so far unknown usefulness of parameters such as median F-wave abnormalities and residual latency, terminal latency index and sensory nerve action potential (SNAP) amplitude was assessed; these parameters were not found sensitive enough, yet high specific (SNAP amplitude) or high sensitive yet low specific (F-wave abnormalities, residual latency and terminal latency index) and are therefore of little value in the early clinical electrodiagnostic evaluation of patients with CTS. Finally, in the patients studied, some degree of axonal loss for motor, sensory and sympathetic median nerve fibers was found in 42% of cases and 6 patients had a double-crush syndrome and 6 others had a concomitant ulnar neuropathy at the elbow.