A case of babesiosis in an asplenic individual is reported. A course characterized by fever, haemolysis, hepatitis, depressed mental status and non-cardiac pulmonary oedema was observed. Studies performed on the patient's lymphocytes revealed profound depression in mitogenic responses during her acute disease which returned to normal with recovery. Serum factor(s) were implicated in causing these changes. Review of the literature on babesiosis in asplenic hosts revealed European patients with disease caused by bovine species of Babesia are at significantly higher risk of a fatal outcome than North Americans with disease caused by murine species.