The recently reported highly sensitive method for assay of acetyl-CoA:arylamine N-acetyltransferase (EC 2.3.1.5) [H. H. Andres, A. J. Klein, S. M. Szabo, and W. W. Weber (1985) 145, 367-375] has been adapted for determination of pyruvate dehydrogenase activity. This method provides an improvement in sensitivity over extant spectrophotometric methods and circumvents limitations of assays using radioactive pyruvate. In addition, the assay is simple and inexpensive and can be readily adapted for measurement of enzyme activity in crude tissue extracts or homogenates.