The pKavalues of pyridine, 2-t-butylpyridine, and 2,6-di-t-butylpyridine have been measured in aqueous solutions of methanol, ethanol, and 2-propanol at concentrations of alcohol ranging up to 70 vol %. The data support the conclusion that the base weakening effect of the alkyl groups in 2,6-di-t-butylpyridine is due to steric inhibition of solvation. © 1968, American Chemical Society. All rights reserved.