An approach to the calculation of molecular electronic structures, solvation energies, and p K values in condensed phases is described. The electronic structure of the solute is a described by density functional quantum mechanics, and electrostatic features of environmental effects are modeled through external charge distributions and continuum dielectrics. The reaction potential produced by a model of the molecular charge distribution is computed via finite-difference solutions to the PoissonαBoltzmann equation and incorporated into the self-consistent field procedure. Here we report results on three sets of organic acids, whose p K values range over 16 pH units. The first set a provides models for ionizable side chains in proteins; the second set considers the effects of substituting one to three chlorine atoms for hydrogens in acetic acid; and the final set w x consists of 4-substituted-bicyclo-2.2.2 -octanecarboxylic acids. Successful prediction of ''absolute'' p K values places stringent requirements on the computation of gas-phase a proton affinities and on the response to solvation. In some cases the current model shows substantial errors, but overall the results and trends are in good agreement with experiment. Prospects for extending this approach to more complex systems such as proteins are briefly discussed.