Local skin reactions (chancres) developed at the sites of inoculation with Trypanosoma evansi in rabbits and calves. Trypanosomes multipled in the dermal collagen and, in the rabbit, were present in large numbers by 7 days after infection. Thereafter, however, numbers decreased and few parasites were observed by 11 days after infection. The presence of trypanosomes in the skin caused an extensive inflammatory reaction with disruption of collagen, oedema, necrosis of the skin and increases principally in neutrophils and lymphocytes. In calves, similar changes were observed although there were fewer trypanosomes present in the chancre and the cellular involvement was less extensive than that seen in the rabbit. This early extracellular proliferative phase of development of T. evansi may be of importance in naturally transmitted infections both in the initial establishment of the parasite in the mammalian host and in enabling the parasite to increase the numbers of antigenic variants expressed before the parasites invade the general circulation.