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Several isoperoxidase activities (EC 1.11.1.7. donor: H2O2 oxidoreductase) were detected in branch extracts of the cardon cactus (Pachycereus pringlei) of the Sonoran Desert, Mexico. The whole enzyme activity in the crude extract was separated into several anionic and cationic isoenzymes. These isoforms exhibited characteristics similar to those of other plant peroxidases, i.e. i) optimal pH, ii) high activity when using guaiacol as hydrogen donor, iii) lower V(max) for DOPA and iv) isoperoxidases were inactivated at high concentrations of the substrate hydrogen peroxide. However, cardon peroxidases were denatured at 70-degrees-C. In FPLC Mono S, the main active fractions were separated into an anionic and two cationic isoperoxidases. When using isoelectric focusing, the anionic isoperoxidase was separated into two bands with slightly different isoelectric points. The partial purification of the crude extract using ammonium sulfate fractionation showed a highly atypical behavior, yielding a purification factor of 12 at 40-90% saturation range.