In vivo imaging of bone marrow using a custom-built fluorescence confocal/multiphoton microscope revealed that pre-B-cell acute lymphoblastic leukemia (ALL) cells preferentially home to bone marrow vessels that express the adhesion molecule E-selectin and Cxcl12 (Sipkins et al., 2005). The gene discussed is CXCL12; the disease is acute lymphoblastic leukemia.