The genotoxicity of a pyrene oxide, 1-nitropyrene (NP) oxides and other related compounds was examined in the hepatocyte primary culture (HPC)/DNA repair test. Pyrene 4,5-oxide and both 1-NP-4,5-oxide and 1-NP-9,10-oxide elicited clearly positive responses of DNA repair. In this assay, 1-NP itself was weakly positive. However, other related chemicals such as pyrene, 1-nitro-3-hydroxypyrene, 1-nitro-6-hydroxypyrene, and 1-nitro-8-hydroxypyrene did not generate positive responses.