Hydrogen peroxide is an ubiquitous metabolite in living systems, produced at increased levels in a variety of pathological situations. Therefore suppressing or at least controlling H2O2 production is important. Catalase enzymes can convert hydrogen peroxide into water and dioxygen and a similar role can be played by transition metal ions or some radiopharmaceuticals. (1) TcO4-, (2) Tc-99m mercaptoacetyltriglycine (MAG3) and (3) Tc-99m methoxyisobutylisonitrile (MIBI) were each tested for their ability to catalyse the disproportionation of hydrogen peroxide in the presence of the added base imidazole. It was found that (2) and (3) exhibit acceptable catalase-like activity compared to the Tc-99m pertechnetate.