The reduction of 21 weak acids, HA, has been studied in dimethyl sulfoxide. The acids included CH, NH and OH acids and their pK(a)(DMSO) values ranged from 6.4 to 19.8. When studied with a freshly polished platinum electrode, all of the NH and OH acids are reduced to form the conjugate base of the acid (A(-)) and dihydrogen. In cyclic voltammetry, the reduction peak on the forward sweep is accompanied by an oxidation peak on the return sweep and the half-wave potential, taken as the mean of the cathodic and anodic peak potentials, was found to be very close to the calculated half-wave potential based on the formal potential for the HA/A(-),H-2 couple for most of these acids. The rate-determining step in the reduction is thought to be a type of dissociative electron transfer whereby HA is reduced to A- plus a hydrogen atom adsorbed on the platinum surface. Consonant with this idea is the observation that no reduction is seen when a non-catalytic surface such as glassy carbon is used. The CH acids fell into several categories. The first included 2,2,5-trimethyl-1,3-dioxane-4,6-dione and malononitrile which behave very similarly to NH and OH acids of similar acidity. 1,3-Diphenyl-1,3-propanedione (completely enolized) and triacetylmethane (68% enolized) react as OH acids with the complication that with the former, reduction to the radical anion occurs in the same potential region as the reduction as an acid. The CH acids ethyl nitroacetate and 2,4-pentanedione (partially enolized) appear to require tautomerization to OH acid forms prior to reduction. Finally, nitromethane shows little indication of reduction as an acid at platinum and is reduced instead to the radical anion which undergoes rapid following reactions.