Peroxynitrite (ONOO-) is a powerful oxidizing agent that forms in a reaction of nitric oxide (NO*) and superoxide (O2-*). We have investigated ONOO--induced DNA damage using deoxynucleosides and oligonucleotides as model substrates, with particular attention paid to the oxidation of 8-oxodG by ONOO-. With regard to deoxynucleosides, ONOO- was found to have significant reactivity only with dG; dA, dC, and dT showed minimal reactivity. However, two of the major products of ONOO--induced oxidation of dG (8-oxodG and 8-nitroG) were both found to be significantly more reactive with ONOO- than with dG. In the context of an oligonucleotide, we observed a concentration-dependent oxidation of 8-oxodG to at least two types of products, one appearing at ONOO- concentrations of </=100 microM and the other at concentrations of >/=500 microM. We also examined the susceptibility of these oxidation products to repair by FaPy glycosylase, endonuclease III, uracil glycosylase, and MutY. FaPy glycosylase, which recognizes 8-oxoG as its primary substrate, was the only enzyme that exhibited an efficient reaction with 8-oxodG oxidation products at low ONOO- concentrations (</=100 microM); the product(s) formed at ONOO- concentrations of >/=500 microM either was not recognized or was poorly repaired by the enzymes. While processing of the lesions was inefficient with endonuclease III and not apparent with uracil glycosylase, the excision of A opposite an 8-oxoG lesion by the enzyme MutY was not affected by the reaction of 8-oxoG with ONOO-. In addition to demonstrating the complexity of ONOO- DNA damage chemistry, these results suggest that 8-oxodG may be a primary target of ONOO- in DNA.