Interleukin 8 (IL-8) is produced by various cells upon stimulation and influences a variety of functions of leukocytes in particular neutrophils. Systemic administration of IL-8 induces a rapid neutropenia associated by sequestration of neutrophils in the lung that is followed by a neutrophilia characterized by the rapid release of neutrophils from the bone marrow. These cells are released predominantly from the bone marrow venous sinusoids. In addition, several studies have shown the potential role of IL-8 in hematopoiesis and trafficking of hematopoietic stem cells. Systemic administration of IL-8 induces a rapid mobilization of progenitors from the bone marrow with long-term myelo-lymphoid repopulation capacity. It has been employed clinically to mobilize hematopoietic progenitor cells into the peripheral blood and used for autologous or allogeneic bone marrow transplantation. The mechanism for these effects of IL-8 is largely speculative. This report summarizes current ideas on the possible mechanisms how IL-8 influences cell trafficking in and from the bone marrow.