AbstractStoichiometric and, in most cases, absolute rates of coupling of a series ofm‐ andp‐substituted benzenediazonium ions with 2,3‐dihydroxynaphthalene‐6‐sulfonate ion (1) have been determined (i) at pH 5.6 (when one OH group is partly monoionized) and (ii) at pH 9.9 (when one OH group is completely ionized and the second slightly so). The rates at both pH values correlate with the σ+parameter (except for the most reactive ArN 2+at pH 9.9) and the contributions of the two reactive forms of the coupler evaluated. Detailed pH dependences of the coupling rate of thep‐chlorobenzenediazonium ion with (1) reveal a strong interaction between (1) and the borate ion, which strongly influences the coupling rate. Coupling rates have also been measured for both diazonium ions and couplers of importance in the diazo reprog