We used in vitro evolution to obtain RNA molecules that specifically recognize and bind with high affinity to the oxidative lesion 7, 8-dihydro-8-hydroxy-2'-deoxyguanosine (8-oxodG) in DNA. A pool of approximately 10(15) RNA molecules containing a random insert of 45 nucleotides in length was subject to 10 successive rounds of chromatographic enrichment using an 8-oxodG affinity matrix, reverse transcription, PCR amplification, and RNA synthesis. Selected RNA molecules bind to 8-oxodG located at the 3' terminus (Kd </= 270 nM) or in the center (Kd </= 2.8 microM) of a 19-nt strand of DNA, with no detectable affinity for the corresponding dG-containing DNA sequences. These 8-oxodG-binding RNAs will be used to monitor levels of 8-oxodG in DNA from biological sources and should provide a unique method for evaluating oxygen-mediated DNA damage. This approach should be applicable for the creation of RNA molecules that can bind to and identify the different modifications of DNA produced by a variety of environmental agents.