It has been shown that the tumour microenvironment confers resistance to chemotherapy. Specifically, it was previously reported that adhesion of haematopoietic tumour cells to fibronectin (FN) via beta1 integrins confers a multi-drug resistance phenotype commonly referred to as cell adhesion mediated drug resistance. The present study showed that the pro-apoptotic BCL-2 family member Bim was reduced when leukaemia cells were adherent to FN via beta1 integrins. beta1 integrin-mediated regulation of Bim in K562 cells was demonstrated to be partly a result of increased proteasomal-mediated degradation of Bim protein levels, and proteasome inhibitors prevent Bim degradation. Increased degradation of Bim was not related to activation of the mitogen-activated protein kinase pathway, as adhesion of K562 cells caused a reduction in phospho-extracellular signal-related kinase (ERK)1/2 levels. In addition, pharmacological inhibition of MAP/ERK (MEK) with PD98059 did not increase Bim levels. Reducing Bim levels by short hairpin RNA targeting inhibited imatinib and mitoxantrone-induced cell death. These results showed that beta1 integrin-mediated adhesion regulates Bim degradation and may contribute to the minimal residual disease associated with many haematopoietic malignancies. Together our data indicate that disrupting beta1 integrin-mediated regulation of Bim degradation may increase the efficacy of drugs, including imatinib, used to treat haematopoietic malignancies.