We have substantially improved a procedure that we previously described for producing C-13/N-15-labeled DNA (Chen et ah, FEES Left. 436, 372-376, 1998) to provide an economical and straightforward approach to the preparation of labeled DNA. The conditions for the PCR reactions have been optimized to permit the use of low concentrations of the costly labeled dNTPs (50 muM for each). In addition, a rapid and high-yield purification procedure has been developed that allows us to obtain a high yield of very pure labeled DNA. These modifications to our original procedure permit us to obtain 1.9 mg of an 18 bp DNA oligomer from 20 nag of dNTPs (ca. 10% yield from the starting dNTPs). This is sufficient material for the preparation of 0.4 mM sample in a volume of 400 mul. In summary, this procedure is a cost-effective, time-efficient procedure for the production of labeled DNA for NMR studies.