The acid dissociation constants of phenylephrine, synephrine, and tyramine were investigated by the new spectrophotometric method of Edsall. Epinephrine was studied by a titration and complexation method. It is concluded from analysis of the spectral data that the phenolic function is a stronger acid than the alkylammonium group. This is contrary to the accepted assignment of acid strengths to these acid functions. The spectrophotometric data were analyzed for the individual microscopic dissociation constants and the degree of dipolar character is reported.