The formation and properties of poly(phenylenediamine) colloidal dispersions were investigated. Oxidative dispersion polymerization of 1,3-phenylenediamine dihydrochloride stabilized with poly(N-vinylpyrrolidone) was taken as a reference experiment. Conductivity, temperature, and acidity of the reaction mixture were recorded during the polymerization. Oxidations of all three phenylenediamine bases, of corresponding dihydrochlorides, and of dihydrochlorides in excess acid are compared. The effect of the nature of steric stabilizer on the course of polymerization was found to be marginal. Dispersion polymerization was observed to proceed faster than the precipitation one. Dynamic light scattering was used to assess particle sizes in poly(phenylenediamine) dispersions. The results are discussed in relation to an analogous polymerization of aniline leading to polyaniline dispersions. Copyright 2001 Academic Press.