Conduct of a large, multicenter trial of the aldose reductase inhibitor zenarestat provided data on the reproducibility of multiple electrophysiologic (nerve conduction studies, NCS) and quantitative sensory (QST) tests. Baseline and 12-month electrophysiologic data from approximately 1100 patients at multiple centers were available for analysis. Intersite variability contributed minimally to overall test variance. All NCS tests were highly reproducible. Cool thermal and vibration QST thresholds, as measured by CASE IV instrumentation, were also highly reproducible. Intersubject variance accounted for the majority of variance for all parameters measured. Repeating NCS and QST measures decreased sample sizes needed to show statistical significance. Consideration of these observations, particularly with regard to QST, should aid in the design of future clinical trials investigating neuropathy.