Human in vitro angiogenesis assay. Photomicrographs demonstrate tubule formation in the human in vitro angiogenesis assay. (top left panel) Stimulation of tubule formation with the addition of VEGF. (bottom left panel) Inhibition of tubule formation with the addition of suramin. (top right panel) No treatment (NT) control without added cytokines or inhibitors. (bottom right panel) Stimulation of tubule formation by plasma of a myeloma patient. Pictures obtained at 12.5 × 0.04 (magnification/aperture).