Attention is drawn to some erroneous and incomplete pieces of information on 99Mo-99mTc generator kinetics published in the literature. The assumption that 99mTc is eluted completely from the generator leads to the incorrect 99TmTc activity-time curve plotted in some papers. It is shown that the time at which 99mTc activity in the generator reaches the maximum value depends on the efficiency of 99mTc separation. The expression derived on by authors allows the prediction of 99mTc activity available in the second separation performed several hours after the previous separation.