Insulin-like growth factor-1 (IGF-I) is a growth and survival factor in human multiple myeloma (MM) cells. Here we examine the effect of IGF-I on MM cell adhesion and migration, and define the role of ß1 integrin in these processes. IGF-I increases adhesion of MM. 1S and OPM6 MM cells to fibronectin (FN) in a time-and dose-dependent manner, as a consequence of IGF-IR activation. Conversely, blocking anti-ß1 integrin monoclonal antibody, RGD peptide, and cytochalasin D inhibit IGF-I-induced cell adhesion to FN. IGF-I rapidly and transiently induces association of IGF-IR and ß1 integrin, with phosphorylation of IGF-IR, IRS-1, and p85PI3-K. IGF-I also triggers phosphorylation of AKT and ERK significantly. Both IGF-IR and ß1 integrin colocalize to lipid rafts on the plasma membrane after IGF-I stimulation. In addition, IGF-I triggers polymerization of F-actin, induces phosphorylation of p125FAK and paxillin, and enhances ß1 integrin interaction with these focal adhesion proteins. Importantly, using pharmacological inhibitors of phosphatidylinositol 3-kinase (PI3-K)(LY294002 and wortmannin) and extracellular signalregulated kinase (PD98059), we demonstrate that IGF-I-induced MM cell adhesion to FN is achieved only when PI3-K/AKT is activated. IGF-I induces a 1.7–2.2 (MM. 1S) and 2–2.5-fold (OPM6) increase in migration, whereas blocking anti-IGF-I and anti-ß1 integrin monoclonal antibodies, PI3-K inhibitors, as well as cytochalasin D abrogate IGF-I-induced MM cell transmigration. Finally, IGF-I induces adhesion of CD138+ patient MM cells. Therefore, these studies suggest a role for IGF-I in trafficking and localization of MM cells in the bone marrow microenvironment. Moreover, they define the functional association of IGF-IR and ß1 integrin in mediating MM cell homing, providing the preclinical rationale for novel treatment strategies targeting IGF-I/IGF-IR in MM.