Cellular DNA repair systems are induced whenever DNA is damaged. Reactive oxygen species (ROS) are generated, in vivo, in the tissues as a result of regular cellular metabolism or after exposure to oxidizing agents, such as ultraviolet (UV) irradiation. It has been suggested that ROS mediate DNA damage. The objectives of the study were as follows: (1) to investigate whether hydrogen peroxide (H2O2), the commonly occurring cellular ROS, induces DNA repair as a response to the damage it probably causes; (2) to evaluate whether H2O2-induced DNA repair, if present, is signaled through a Ca2+-dependent pathway via the tyrosine kinase signal transduction. H2O2 was found to induce DNA repair in human peripheral blood mononuclear cells (PBMCs) in a dose-dependent manner. The recovery of RNA synthesis, which occurred after DNA repair, confirmed that transcribable DNA was repaired. The inhibition of tyrosine kinase activity by genistein reduced the DNA repair significantly. Furthermore, H2O2 caused a dose-dependent significant rise in cytosolic calcium ((Ca2+)i). H2O2 also induced a small rise in (Ca2+)i of cytosolic Ca2+-depleted cells, probably reflecting the release of Ca2+ from internal stores. Genistein inhibited both Ca2+ influx and Ca2+ release from internal stores. In summary, H2O2 induced a DNA repair synthesis that was in part Ca2+ dependent and signaled via tyrosine kinase. The changes in DNA repair paralleled changes in (Ca2+)i. The H2O2-induced (Ca2+)i rise was mostly the result of influx, but to some degree it was also due to the translocation of Ca2+ from internal stores.