We have developed a simplified assay for the enzyme N-acetyltransferase, based upon the loss of fluorescence after acetylation of the substrate p-aminobenzoic acid. This method is sufficiently sensitive to permit the quantitation of N-acetyltransferase activity in 10(5) human lymphocytes. Using this method, we have compared the level of N-acetyltransferase activity in lymphocytes from adult per...