A research submitted to the Faculty of Veterinary Medicine in partial fulfilment of the requirement for the award of the degree of Master of Science (M.Sc.) in Veterinary Medicine of University of Nigeria, Nsukka. The effects of Trypanosoma congolense, Trypanosoma brucei and their mixed infection on parvoviral vaccination was experimentally studied in mongrel dogs. Twenty mongrel dogs of mixed sexes and approximately 4-6 months of age weighing an average of 6.5 kg were used for the experiment. They were acclimatized for three weeks prior to commencement of the study during which time routine treatments and screening were done. The dogs were kept in cages in a fly proof experimental animal house and were adequately fed and given water ad libitum. The twenty mongrel dogs were divided into five groups of four dogs each. Group A were vaccinated and uninfected, group B were unvaccinated and uninfected, group C were infected with T. congolense, and vaccinated, group D were infected with T. brucei and vaccinated and group E were infected with T. congolense and T. brucei and vaccinated. Clinical signs observed in the dogs were as pyrexia, anorexia, emaciation, lethargy, rough hair.