Focal contacts are best seen in living cells by reflection-interference microscopy (A). In this technique, light is reflected from the lower surface of a cell attached to a glass slide, and the focal contacts appear as dark patches. (B) Immunofluorescence staining of the same cell (after fixation) with antibodies to actin shows that most of the cell's actin filament bundles (or stress fibers) terminate at or close to a focal contact. (Courtesy of Grenham Ireland.)