The cytoskeleton is a central and vital structure of eukaryotic cells. It consists of a dynamic network of partially interconnected polymers. This extended network controls the mechanical properties of animal cells, serves as intracellular transport "pathways", and plays a prominent role in cell motility, proliferation, and adhesion. In order to evaluate the action of laser irradiation on the cytoskeleton and proliferation of endothelial cells, rabbit aortic endothelial cells (RAEC) were irradiated with 685-nm low-level laser (20 mW output power). Fluorescent dye rhodamine-phalloidin staining was used to visualize the effect of laser irradiation on actin filaments. Irradiation with 8 J/cm(2) was performed four times at 12-h intervals for 24 min. Cells cultured under low fetal bovine serum condition (5% FBS) for 7 days presented actin staining predominantly in the cortical membrane region and a few actin filament stress fibers. However, the formation of stress fibers similar to those of control cells increased significantly in irradiated cells. It was concluded that laser irradiation induces changes in the cytoskeleton of endothelial cells through the reorganization of actin filaments and neo-formation of stress fibers, allowing evident cellular proliferation.