A study has been made of the solid phase thermal cyclization of some poly(amino acids) (PAA) and compounds modelling chain fragments of PAA differing as to degrees of imidization and to the type of alternation of 0-carboxylamide groups and imide cycles in a molecule. It has been found that the specific nature of the process of polycyclodehydration, i.e. degrees of cyclization reaching limiting values with time, is typical also of the imidization of low molecular analogues of PAA (MW 40–1000), which means that it does not seem to stem solely the polymeric nature of the reagent. In the light of the experimental results it is suggested that the mode of formation of hydrogen bonds in o-carboxyamides may be an essential factor largely determining the imidization kinetics.