Aspects of the patho-physiology of ovine trypanosomiasis were studied among 16 West African dwarf rams successfully treated against acute experimental trypanosomiasis due to single or mixed infections of Trypanosoma congolense and T. br. brucei. Body weight, body temperature, packed cell volume, and testicular diameter values recorded during the infection period showed appreciable return to normal values after a single diaminazine aceturate treatment. However, animals remained unthrifty and showed poor weight gains and high mortality rates after 12 weeks. Concurrent broncho--pneumonia was commonly associated with the post-treatment mortalities. Mortality among the mixed infection group was higher than in the T. congolense and T. br. brucei groups. It was concluded that the effect of trypanosomiasis on the sheep was marked and may require an extended recovery period, even after a successful single dose of diaminazine aceturate treatment.