AbstractExposure to jet fuel damages DNA and results in a number of physiological changes in liver, lung, immune, and neurological tissue. In this study the single‐cell gel electrophoresis assay or comet assay was used to compare the DNA damage in human peripheral lymphocytes produced by three jet propulsion fuels: JP‐8, JP‐5, and JP‐8+100. These fuels consist of complex mixtures of aliphatic, aromatic, and substituted naphthalene hydrocarbons. Two exposure times were investigated which correspond to estimated occupational exposure times and concentrations of fuels were used that were based on previous fuel toxicity studies. Analysis of samples for the extent of DNA damage as determined by tail moment and percent tail DNA was performed on exposed cells following a brief recovery time. All fuels produced significant increases in DNA damage; however, only JP‐8+100 was genotoxic at the lowest exposure concentration (1:500). At the highest exposure concentration (1:75), the mean tail moments for JP‐8 and JP‐8+100 (32.041 ± 2.599 and 45.774 ± 4.743, respectively) were significantly greater than for JP‐5 (1.314 ± 0.474). These results indicate that JP‐8+100 is the most potent inducer of DNA damage in human peripheral lymphocytes and that both JP‐8+100 and JP‐8 are capable of damaging lymphocyte DNA to a greater extent than JP‐5. Environ. Mol. Mutagen. 40:18–23, 2002. © 2002 Wiley‐Liss, Inc.