Model structure. The compartments S, CG, PGP, MGP, and GRA represent stem cells, CFU-GM, proliferating granuloid precursors (myeloblasts, promyelocytes, myelocytes), maturing granuloid precursors (metamyelocytes, banded and segmented neutrophils), and peripheral neutrophils, respectively. GCSF_C and GMCSF indicate the circulating levels of G-CSF and GM-CSF, respectively. GCSF_S represents the subcutaneous compartment for exogenous rhG-CSF. CX represents the chemotherapy. Bold black and gray lines indicate cell and cytokine flux, respectively. Thin dashed and solid lines indicate the afferent and efferent parts of regulatory loops, respectively. Numbers in circles indicate the basic modes of drug action: (1) acute loss of cells, (2) enhanced mitotic activity, (3) accelerated differentiation, and (4) increased rate of release to the peripheral blood stream.