Technetium-99m-labelled red blood cells (RBC) have been used as radiopharmaceutical in nuclear medicine. The influence of drug interaction in this labelling process has been described along with the biological effects of tobacco on the labelling of blood elements with technetium-99m. The labelling of RBC and plasma proteins can be decreased in presence of tobacco. This can be due to either a direct or indirect effect (reactive oxygen species) of tobacco by (i) oxidation of the stannous ion, (ii) possible damages caused in plasma membrane and/or (iii) possible chelating action on the stannous and/or pertechnetate ions.