Proton adsorption isotherms derived from potentiometric titration of high surface area alpha aluminas were deconvoluted to yield proton affinity distributions. The results reported provide another view and additional support to the conclusion reached by Mao and Vannice [Appl. Catal. A, 111 (1994) 151] that these materials prepared by topotactic transformation of diaspore have surface properties unlike those of either low surface area alpha-Al2O3 or transition aluminas.