The effects of pH on the observed rate constants (k obsd. ) and on the solvolytic dediazoniation product distributions of ethanolysis of 2-, 3-, and 4-methylbenzenediazonium ions (2MBD, 3MBD, and 4MBD, respectively) were determined by a combination of spectrophotometric (UV/Vis) and chromatographic (HPLC) techniques. The variation of both k obsd. and product yields with pH follow S-shaped curves with inflection points at pH ഠ 3.6, depending on solvent composition. With increasing pH, k obsd. values increase by factors of up to about 4 (2MBD), about 3 (3MBD), and about 50 (4MBD) with respect to the k obsd. values at low pH. HPLC analyses of the reaction mixtures show that only heterolytic products are obtained at low pH, indicating that solvolytic dediazoniation takes place through an ionic mechanism, but an increase in