The ability of dicarboxylic acids to interact with amino acids to form monomeric or polymeric products has been observed by means of DSC and TG techniques. The solid-solid reactions have been carried out, the associated DELTAH values evaluated, and the reaction mechanism elucidated. In the solid state phthalic acid interacts with amino acid to form the monomeric product N-phthalylaminoacid, by losing two water molecules. The product formed has been characterized from its IR and NMR spectra.