Recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) has been used in two clinical studies at the Christie Hospital in Manchester, United Kingdom. Short daily "bolus" injections (over 30 min) were associated with serious toxicity which included bone pain, pruritus and pericarditis. In contrast, continuous infusions did not cause any toxicity and produced significantly higher increments of the peripheral neutrophil counts. rhGM-CSF reduced the period of life-threatening neutropenia following high-dose i.v. melphalan (120 mg/m2). Also, rhGM-CSF shortened the duration of thrombocytopenia induced by this chemotherapy to less time than has been seen historically in conjunction with autologous bone marrow rescue.