Reactive haemophagocytic syndrome (RHS) is a disorder characterized by systemic proliferation of non-malignant histiocytes occurring most commonly in patients with pre-existing immunological abnormalities or neoplasms. Patients, particularly those with immunosuppression, often have a rapidly progressive fatal course. Treatment is directed at the underlying disorder. In the absence of identifiable cause, the therapy is less satisfactory. We report here three cases of RHS successfully treated with high-dose gamma-globulin therapy. Two of the three patients were immunocompromised and the third occurred during pregnancy. The improvement occurred within 24-72 h and all patients recovered. High-dose i.v. gamma-globulin therapy may be beneficial in RHS.