Video time lapse microscopy demonstrates that the morphologically distinct HPB-ALL pseudopodia are due to aberrant extension, rather than aberrant pseudopodial retraction. Cells were "untreated," subjected to electroporation in control buffer ("mock electroporated"), or electroporated in the presence of C3 (25 μg/ml, "C3 electroporated"). Cells were then plated onto VCAM-1 and let spread for 1 hr (as described in Materials and Methods) while being recorded by a CCD camera and time lapse VCR. Numbers in lower left corners of images denote time elapsed in minutes. Arrowheads identify pseudopodia of spreading cells. Initial magnification was 400×.