OBJECTIVE Rho kinases (ROCKs) are involved in regulating a variety of physiologic functions including cytoskeletal reorganization, migration, adhesion, survival and proliferation. They do so via activating several different downstream substrates such as myosin light chain phosphatase, LIM kinase and ezrin/radixin/moesin proteins. To date, most of the conclusions with regard to the function of ROCKs have involved the use of cell line models, pharmacologic inhibitors and dominant negative approaches. Importantly, the role of ROCK in hematopoiesis or leukemogenesis in the context of whole organism remains poorly understood. RESULTS Recent studies utilizing mice deficient in the expression of ROCK1 have begun to shed some light into the physiologic role(s) of ROCK in both normal and abnormal hematopoiesis. Findings, thus far, suggest that ROCK plays an essential role in regulating growth and survival in different hematopoietic lineages via distinct mechanisms, in part, by utilizing distinct downstream substrates including maintaining the activation of tumor-suppressor genes. CONCLUSIONS In blood cells, emerging data suggest that ROCK plays an essential role in negatively regulating inflammatory and erythropoietic stress and positively regulates the growth and survival of leukemic cells.