Kinetics and mechanism of the alkaline hydrolysis of two dihydroxamic acids, oxalo and malonodihydroxamic acids, have been studied in 25% (v/v) DMSO at 75 degrees C. The solvent, salt, temperature, and solvent isotopic effects have been examined. Correlation of reaction rate with the acidity function (H-) and these effects indicate a pathway involving the rate-limiting formation of a tetrahedral intermediate that decomposes to give products.