Mixed T. congolense and T. brucei appeared in mice when proboscis from 3 field collected G. pallidipes were individually inoculated into mice. One of these flies had earlier been shown by dissection, to have T. congolense and the other two had T. brucei infection. A comparison of the growth rates of T. congolense and T. brucei in mice revealed that T. brucei always overshadowed T. congolense. These observations highlight the significance of multiple trypanosome infections in the epidemiology of African trypanosomiasis.