The existence of a bone marrow renin–angiotensin system (RAS) is evidenced by the association of renin, angiotensin converting enzyme (ACE), and angiotensin (Ang) II and its AT1 and AT2 receptors with both normal and disturbed haematopoiesis. The expression of RAS components by rat unfractionated bone marrow cells (BMC), haematopoietic-lineage BMC and cultured marrow stromal cells (MSC) was investigated to determine which specific cell types may contribute to a local bone marrow RAS. The mRNAs for angiotensinogen, renin, ACE, and AT1a and AT2 receptors were present in BMC and in cultured MSC; ACE2 mRNA was detected only in BMC. Two-colour flow fluorocytometry analysis showed immunodetectable angiotensinogen, ACE, AT1 and AT2 receptors, and Ang II, as well as binding of Ang II to AT1 and AT2 receptors, in CD4+, CD11b/c+, CD45R+ and CD90+ BMC and cultured MSC; renin was found in all cell types with the exception of CD4+ BMC. Furthermore, Ang II was detected by radioimmunoassay in MSC homogenates as well as conditioned culture medium. The presence of Ang II receptors in both haematopoietic-lineage BMC and MSC, and the de novo synthesis of Ang II by MSC suggest a potential autocrine–paracrine mechanism for local RAS-mediated regulation of haematopoiesis.