Bovine pulmonary artery endothelial cells were labeled with fluorescein phalloidin (Cat. no. F432), which labels filamentous actin, and placed under constant illumination on the microscope with a FITC filter set using a 60× objective. Images were acquired at one-second intervals for 30 seconds. Under these illumination conditions, fluorescein photobleached to about 12% of its initial value in 30 seconds in PBS (left), but stayed at the initial value under the same illumination conditions when mounted using the reagents in the ProLong® Antifade Kit (right, Cat. no. P7481).