In order to more accurately substantiate the assumption that pegfilgrastim alters the balance between IL-12 and IL-10, monocytes, a prominent cellular source of both IL-12 and IL-10, were magnetically purified on day +11 from the peripheral blood of patients treated with pegfilgrastim (24 hours before the anticipated decline of serum pegfilgrastim concentration [16] and coincident with maximal monocyte mobilization) and from cancer patients treated with daily filgrastim (24 hours after the last G-CSF administration). The gene discussed is IL10; the disease is cancer.