Some factors which could adversely affect the integrity of eight routine99mTc radiopharmaceuticals have been investigated. The radiochemical purity of the preparations was determined both under “standard” (reconstitution according to the manufacturer's instructions) and under “experimental” conditions (higher contents of longlived99Tc and copper). The influence of radiolytically produced hydrogen peroxide as well as the effect of introduction of air during the addition of pertechnetate as an example of poor labeling technique were examined. The radiochemical analyses were performed by paper and TL chromatography and electrophoresis.