The acid-catalysed hydrolyses of some para-substituted benzohydroxamic acids have been studied in perchloric, sulphuric, and hydrochloric acids. Plots of the first-order rate-coefficients, k₁, against [H⁺] show maxima which are caused by extensive protonation of the substrate. The mechanism of hydrolysis is found to be similar to that of amides. The protonation behaviour of these compounds correlates better with the amide acidity function H_A than with H₀.