There is evidence that the biodistribution and the pharmacokinetics of 99Tcm radiopharmaceuticals can be modified by some drugs, pathological states, irradiation and surgical procedures. Vincristine have been widely used in various chemotherapeutic protocols in oncology. We are trying to develop an animal model to assess the toxicology in different organs of compounds used as therapeutic drugs. We have studied the effect of vincristine on the distribution of 99Tcm-glucoheptonic acid (99Tcm-GHA) in female mice. After the last dose of vincristine, 99Tcm-GHA (7.4 MBq) was injected, the animals sacrificed and the percentage of radioactivity determined in the isolated organs. The percentage of activity was significantly decreased in the uterus, ovary, spleen, thymus, lymph nodes (inguinal and mesenteric), kidney and heart, but was not significantly altered in the lung, liver, pancreas, stomach, thyroid, brain and bone. Our results can be explained by the metabolic, toxic, therapeutic and immunosuppressive actions of this chemotherapeutic drug.