The formation of reactive oxygen and nitrogen species by rat peritoneal macrophages induced by a low-intensity He-Ne laser radiation (LR) was studied in this work. It was found that the formation of reactive oxygen species, nitric oxide, and peroxynitrite as well as changes in the activity of superoxide dismutase (SOD) depended to a large extent on the LR dose. In particular, it was found that activation of SOD at low LR doses was accompanied by nitric oxide level increase, while the level of peroxynitrite showed no significant changes. On the other hand, an enhanced LR dose inhibited the enzyme, and this was accompanied by peroxynitrite accumulation. All the measurements were carried out the day after LR treatment. The revealed regularities consequently demonstrate the existence of a deferred LR action on macrophages associated with the production of reactive oxygen and nitrogen species.