Electrolytic labelling procedures have been reported for various99mTc radiopharmaceuticals which differ widely in the choice of the electrodes, working pH, applied voltage and the quantity of current passed. The authors have studied the electrolytic labelling of99mTc EHDP, gluconate and glucoheptonate with MEK extracted99mTc using tin electrodes under different experimental conditions. The results have, shown that these compounds can be efficiently labelled with99mTc in a single step procedure avoiding multiple pH adjustments. Labelling of human serum albumin microspheres suitable for lung imaging with99mTc by the electrolytic method is also reported.