Splenectomy delayed the onset of the anaemia in rabbits infected with either Trypanosoma brucei brucei S42 or T. b. brucei 427 and, particularly in the latter infection, also lessened its severity. Parasitaemias were higher in the 427 infection although, terminally, massive parasitaemias were recorded in the S42 infection. With 51Cr-labelled red cells, it was shown that there was an increase in both splenic sequestration and destruction of red cells in infected animals relative to controls, the degree of sequestration probably being related to the degree of splenic enlargement. Red cell T50 values were virtually unaffected by trypanosomal infection of splenectomized rabbits, and in those splenectomized in mid-infection a marked increase in T50 was observed shortly after the operation. Since the anaemia which eventually developed in the splenectomized animals was not accompanied by a reduction in T50, it is unlikely to be of haemolytic origin. Other possible causes are considered.