Aim of this study is to bring systematic comparison of structure and properties of the redox-active oxidation products of various phenylenediamines prepared under various acidic conditions. According to literature, structure and properties of the phenylenediamine oxidation products depend on the reaction conditions. Various ladder-like structures have widely been accepted in the literature since they can be potentially created from any phenylenediamine isomer. The presence of polyaniline-like structural units, however, has also been reported and often discussed. The conductivity of the reaction products was compared for the oxidation of o-, m- and p-phenylenediamine with ammonium peroxydisulfate in 1 M methanesulfonic acid, water, or in 1 M ammonium hydroxide. The combination of size exclusion chromatography with UV visible, FTIR and Raman spectroscopies allow us to analyze the molecular structure of the oxidation products and to bring significant information on (1) the formation of oligomer and polymer fractions, (2) the content of benzenoid and quinonoid units suggesting the presence of polyaniline-like segments, and (3) the participation of phenazine-like constitutional units indicating the formation of polycyclic structures. The oxidation products have also been tested for their cytotoxicity in order to estimate their application potential in biomedicine. The dilution of extracts below 5% concentration was generally needed to suppress the cytotoxicity. (C) 2017 Elsevier B.V. All rights reserved.