Evidence from cell line-based studies indicates that rho-kinase may play a role in the leukaemic transformation of human cells mediated by the BCR/ABL tyrosine kinase, manifest clinically as chronic myeloid leukaemia (CML). We therefore employed two separate inhibitors, Y-27632 and fasudil, to inhibit the activity of rho-kinase against ex vivo CD34(+) cells collected from patients with CML. We compared the effects of rho-kinase inhibition in those cells with the effects of direct inhibition of BCR/ABL using the specific inhibitor imatinib. We found that inhibition of rho-kinase inhibited the effective proliferation, and reduced survival of CML progenitor cells. When combined with imatinib, rho-kinase inhibition added to the anti-proliferative and pro-apoptotic effects of the BCR/ABL inhibitor. Our studies may indicate therapeutic benefit in some cases for the combination of rho-kinase inhibitors with imatinib.