The characteristics and clinical uses of recombinant colony-stimulating factors (CSFs) are described, and the pharmacist's role as a consultant and educator on biotherapeutic substances is discussed. CSFs stimulate the formation and differentiation of the erythrocytes, neutrophils, eosinophils, basophils, monocytes, and platelets that compose the blood cell population. Recombinant CSFs represent a means by which the numbers of hematopoietic cells can be modulated, thus making these agents potentially useful in treating hematologic and immunologic deficiencies. CSFs also can increase the ability of neutrophils and monocyte-macrophages to protect the body against foreign invasion. Granulocyte macrophage colony-stimulating factor (GM-CSF) has increased host defenses in acquired immunodeficiency syndrome patients with Kaposi's sarcoma; increased neutrophil, platelet, and erythrocyte counts in preleukemic patients; and increased neutrophil counts in patients with aplastic anemia. GM-CSF and granulocyte colony-stimulating factor (G-CSF) have appeared to alleviate the drastic decrease in neutrophil counts associated with cytotoxic chemotherapy. G-CSF also has shown promise in stimulating neutrophil production in patients with transitional cell carcinoma, congenital agranulocytosis, and hairy-cell leukemia. Mild adverse effects such as fever, chills, rash, fatigue, myalgia, and bone pain are associated with GM-CSF therapy; G-CSF therapy is associated mostly with mild to moderate bone pain. Areas of education for pharmacists working with biotherapeutic substances include stability, storage temperature, drug interactions, novel drug-delivery systems such as monoclonal antibodies or liposomes, variations in biologic activity, and the evolving nature of the information about these investigational drugs. The pharmacist can anticipate an increasing role as a consultant on the use of CSFs and other biotherapeutic substances.(ABSTRACT TRUNCATED AT 250 WORDS)