Electromotive force (emf) measurements of the cell without a liquid junction of the type PtH-2TAPSO (m(1)) + NaTAPSOate (m(2)) + NaCl (m(3))AgClAg were made at intervals of 5K from 5 degrees C to 55 degrees C, including 37 degrees C, with stoichiometric molalities m(1)=m(2)=m(3) ranging from 0.01 to 0.1 mol . kg(-1). At 25 degrees C, pK(2) is 7.635, and consequently buffer solutions of TAPSO and its salt (NaTAPSOate) are useful for pH control in the region pH 6 to 8. The second dissociation constant (pK(2)) of TAPSO can be expressed by the equation 2254.0057/(T/K)-4.9783+0.88672 In(T/K), with a standard deviation of +/-0.0008. The zwitterionic buffer TAPSO is represented as 3-[N-(tris(hydroxymethyl)methyl)amino]-2-hydroxypropanesulfonic acid, a derivative of the parent compound taurine.