The traumatic or surgical cutting of a long bone is immediately followed by a sequence of repair processes in which the osteogenic cells of the periosteum start to proliferate and differentiate in osteoblast cells. In this work, we explored the influence of a He-Ne laser on osteogenesis after a controlled surgical fracture. We used young male adult Wistar rats (of mass between 250 and 300 g). The fracture was provoked by piercing a 2-mm-diameter hole in just one cortical tibia surface. Laser treatment was started 24 h after the surgery. The animals were separated into three groups, for different radiation doses, and after daily applications, they were sacrificed at 8 or 15 days. Light and electron microscopies revealed that the laser treatment of the lesion with doses of 31.5 and 94.7 J cm(-2) resulted in the formation of thicker bony trabeculae, which indicates a greater synthesis of collagen fibers and therefore that the osteoblastic activity was increased by the low-energy laser radiation.