The usefulness and accuracy of a portable instrument, the electroneurometer, for measuring distal motor latencies was determined in a prospective study of 28 patients (51 hands) with carpal tunnel syndrome and 10 controls (18 hands). There was a close correlation of distal motor latencies from the electroneurometer with those from formal electrodiagnostic testing. The average distal motor latency of controls was 3.3 ± 0.4 msec, compared with a mean value of 5.2 ± 1.8 msec in symptomatic hands. The sensitivity of the neurometer test alone was 69% (9 false-negatives); when combined with quantitative sensibility testing, sensitivity increased to 84%. Specificity of the neurometer test alone was 100% (no false-positives). The portable electroneurometer is a convenient, painless, inexpensive device for screening patients with carpal tunnel syndrome. Formal electrodiagnostic testing is indicated for differentiation of lesions present at different levels, for detection of subtle sensory changes, and for use in those patients in whom surface electrode usage is ineffective.