There is no nerve conduction study for the thoracodorsal nerve in the literature. A conduction study for this nerve is described. Thirty healthy adults (16 males) with a mean age of 41.5 +/- 10.6 (range, 22-63) years were studied. The thoracodorsal nerve was stimulated at axilla and Erb's point with recording over the latissimus dorsi. The latency was 1.9 +/- 0.4 (range, 1.2-2.7) ms and 3.6 +/- 0.4 (range, 2.8-4.5) ms for the axillary and Erb's stimulations, respectively. The amplitude of the compound muscle action potential was 4.1 +/- 1.8 mv on the right and 3.9 +/- 1.4 mv on the left. The compound muscle action potential ratio was 0.8 +/- 0.12 (range, 0.55-0.99). This study may be useful to evaluate the integrity of the thoracodorsal nerve and to assist in the diagnosis and prognosis of brachial plexus injury.