The production of human blood cells is regulated through a highly complex, coupled set of feedback mechanisms involving, among others, differentiation of cell lines from a common pool of stem cells and hormonal interactions between circulating cells and cells at different stages of maturation. As part of a global modeling project of the full hematopoietic system, we investigate possible pharmaceutical interventions using a structured model for the regulation of blood cells taking the form of a system of nonlinear delay differential equations. This model contains multiple time delays to incorporate maturation and lifespan times of the different cell species, together with feedback control mechanisms relating the circulating cells to the maturation process: some of the delays are therefore state-dependent. Concentrating on the regulation of neutrophils, we analyse the perturbative effects of different chemotherapeutic regimens on equilibrium solutions. We obtain dynamical interpretations for the neutropenic episodes: the influence of scheduling, as well as the remedial use of G-CSF, is particularly emphasized. Parameter estimation and compatibility of the behavior of the solutions of our model with clinical practice will be discussed. Supported by NSERC and FRQNT.