Platelet aggregation leading to a decreased number of thrombocytes and reduced blood serotonin levels can be correlated with parasitaemia as has been observed in goats and cattle infected withT. vivaxY58. Flurbiprofen is a potent anti‐inflammatory agent with antipyretic activity.In vitro, this agent inhibits platelet aggregation and blocks serotonin release. The results of the present study demonstrated that flurbiprofen inhibited the febrile reactions during the acute phase ofT. vivaxinfection, but the drug did not prevent or reverse the associated drop in blood serotonin level during this period. Moreover, it was apparent that flurbiprofen had a deleterious effect on goats infected withT. vivaxY58. The infection in the untreated animals (sixteen out of seventeen goats) followed a rather mild and prolonged course with peaks of parasitaemia during the febrile episodes, whereas in flurbiprofen‐treated goats (five animals), inoculated with the same number of trypanosomes, the parasitaemia was progressive and terminated in early death with disseminated intravascular coagulation at post mortem examination. These observations would seem to confirm the work of previous investigators, suggesting that anti‐inflammatory agents have an aggravatory effect on the course of infection in animals inoculated with various strains of trypanosomes. Important differences exist, however, in the relationship between prostaglandin synthesis in the platelets of the goat and in those of other sp