This paper presents the preparation of a radiocolloid that still makes it possible to label leukocytes using its phagocytosis capacity. Given that this function is exclusively of the white blood cells, not being exercised by other blood cells, the use of a stannous fluoride radiocolloid labeled with 99mTc (F2Sn-99mTc) was tested in order to label leukocytes in whole blood samples. Using cellular separation techniques in density gradients and acquisition of images in gamma camera of radioactivity distribution in Percol, it was observed that the white cells labeling achieved was selective and with high efficiency for leukocytes (in all cases, it was superior to 70%), optimal reproducibility, low cost and low cellular toxicity.