We have investigated the influence of the type of basic catalyst on the mechanisms and kinetics of phenol-formaldehyde reactions in perfectly controlled conditions of synthesis (temperature, stoichiometry and pH). The results obtained using liquid-state physicochemical analysis techniques, such as high performance liquid chromatography, C-13 nuclear magnetic resonance spectroscopy and chemical assays, indicate that the nature of the basic catalyst affects the mechanisms and kinetics of condensation and thus the composition of the reaction medium. The results show that the valence and ionic radius of hydrated cations affect the changes of species in the reaction medium. The catalysts were classified into two families as a function of their behaviour : KOH, NaOH and LIOH, and Ba(OH)(2) and ME(OH)(2). We have found the formation of certain monomers and dimers, particularly ortho-substituted species.