U87MG glioma cells expressing the de2-7 EGFR (or EGFRvIII) were transiently transfected with the lysosomal marker lgp-120 tagged with GFP (green staining). After transfection, cells were incubated with mAb 806-cy3 at 4°C (red staining), before induction of internalization by incubating at 37°C for 0 (top left), 30 (top right), 60 (bottom left) and 120 (bottom right) minutes. Colocalization of mAb 806-Cy3 and lgp-120-GFP in the lysosomes can be clearly observed at 60 and 120 minutes (yellow staining). For further details, please see Johns et al. on page 1911 in this issue.