The inhibitory effects of various nitrogen-containing sugars on porcine kidney trehalase were studied. Validamycin A, validoxylamine A and MDL 25637 were found to be potent, time-dependent inhibitors of the enzyme in vitro. The validoxylamine A-inhibited enzyme showed slow but reversible reactivation over time (t
= 1.2 h). To our knowledge, this is the first report of time-dependent inhibition exhibited by either these particular amino-sugars or a trehalase.