Natural products have been widely used by human beings. However, sometimes the biological effects of these products are not fully known. Chayotte (Sechium edule) is a vegetable used in the folk medicine. Red blood cells (RBC) labeled with technetium-99m (99mTc) have several clinical applications. The aim of this work was to evaluate the influence of an extract of chayotte on the labeling of blood elements with 99mTc using stannous chloride (SnCl 2 ) in the concentrations like to 1.2, 0.006,

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... 05 and 0.0006 µg/ml. The extract of chayote was incubated in various concentrations for 1hour with blood which was withdrawn from Wistar rats. After that SnCl 2 was added and the incubation continued for more 1 h. Elapsed this time 99mTc as sodium pertechnetate (NaTcO 4 ) was toted. The blood was centrifuged and plasma (P) and RBC were isolated, also precipitated with trichloroacetic acid (TCA, 5%) and soluble (S) and insoluble (I) fractions (F) of plasma and cells (C) were determined. The radioactivity (ATI%) was rated in RBC, IF-P and IF-C. The results have showed that extract was able to reduce the radiolabeling using SnCl 2 (0.006, 0.0005 and 0.0006µg/ml). We can speculate that this effect may be on account of the products with oxidant proprieties.