Posterior interosseous nerve conduction was studied by a new method consisting of two different techniques in 40 controls. The motor latency of the brachioradialis and extensor carpi ulnaris was compared after stimulation of the radial nerve, either at the axilla or above the elbow. The nerve branches of the brachioradialis never cross the radial tunnel, whereas those of the extensor carpi ulnaris always cross the radial tunnel. The recording was performed with a coaxial needle electrode after percutaneous axillary stimulation and with surface electrodes after near-the-nerve elbow stimulation. The mean brachioradialis/extensor carpi ulnaris latency difference was 1.3 ms and represented the posterior interosseous nerve conduction in the radial tunnel. Identical values were obtained with both techniques, but the inter- and intraindividual variability was less marked with the elbow technique. Overall, the right/left comparison provided the best diagnostic data because of a normal range limited to only 0.4 ms after elbow stimulation.