NOTES & TIPS 181 among eubacterial species, it appears that inhibitors of PDF activity should act as potent wide-spectrum antibacterial agents. In other words, PDF could be a good target in the context of the recent upsurge in the search for new antibiotics (11, 12). However, to systematically assess the putative inhibitory capacities of such agents on PDF, a new assay is required. The standard assay for PDF (2, 3) is based on the reactivity with ninhydrin of the primary amine of methionine which is unmasked after removal of the N-formyl group from the substrate. In addition to the low sensitivity, high background level, and rather poor specificity of the signal, this assay is very time consuming since the time course of deformylation cannot be directly measured. As a result, several final-time assays must be performed to determine