AbstractThe multilineage hematopoietic effects of IL‐3 appear to be most important for its clinical use comprising especially leucocyte and platelet responses. This was demonstrated to be dose dependent characterising doses of 250 to 500 μg/m2/day subcutaneously as hematopoietic effective and well tolerable. Since preclinical data suggest synergism between IL‐3 and GM‐CSF hematopoietic effects of their sequential administration were evaluated in 15 patients with preserved hematopoietic function. An enhanced stimulation of megakaryopoiesis combined with more pronounced stimulation of granulopoiesis than IL‐3 alone could be demonstrated. The cytokine combination of IL‐3 and GM‐CSF was thus used during chemotherapy induced myelosuppression. Data indicates beyond the known amelioration of myelosuppression by GM‐CSF additional chances to enhance platelet recovery which can be of important clinical impact. © 1992