The purpose of this research was to study the relationship between the Toxocara canis larvae and the transmission of bacteria in mice. Special attention was given to the attempt to understand the mechanisms by which the larvae could play a role in the dissemination of infection. Radioactive isotopes were used to label the Escherichia coli bacteria. Three isotopes were used, one β emitter (32p) and the two others were 59Fe and 51Cr as ɣ emitters. Exposure of the larvae to labelled bacteria, both in vitro and in vivo resulted in obtaining evidence that they could carry the bacteria. When the experiment s were done in vivo, the results strongly suggested that the T. cants larvae were able to disseminate the bacteria from the intestine to all the organs of the animals tested. The attempt to check whether the larvae exposed to the bacteria in a test tube could disseminate bacteria to the organs of mice, showed inconclusive results . Confirmatory experiments were carried out by using bacteriological and serological techniques. Evidence was obtained that the larvae were able to carry and might be able to disseminate the E. coli to the organs of the mouse. The result s will be discussed in relation to the possible dangers of these worms in the dissemination of disease-causing micro-organisms from the intestine to other parts of the body.