Potential genotoxic effects of diffusion flame-derived particulate matters (PMs), known to cause various adverse health problems, doped with iron, one of the representative heavy metals frequently found in the atmosphere, were examined. B6C3F1 mice were exposed to PMs [chamber 1 (low), 100; chamber 2 (middle), 200; and chamber 3 (high), 400 microg/m3] for 6 h/day, 5 days/week for one, two and four weeks in 1.5 m3 whole-body inhalation chambers. Our diffusion flame system produced 94.8 and 5.2% fine PM2.5 and PM10, respectively, with 89% of PM2.5 sized between 0.1 and 0.2 microm. Two cytogenetic endpoints were investigated through chromosomal aberration and supravital micronucleus (SMN) assays. Frequencies of cells with chromosome aberration (%) were observed in time- and concentration-dependent manners except in one-week exposure group, as also observed in SMN study. Generally, noniron flame induced less chromosome aberration than iron-doped flame, an indication that iron particles could potentiate urban PM toxicity. The above results indicate our diffusion flame system generated genotoxic fine PMs, whose effects were potentiated by organometallic particles such as iron. Our system can provide reliable PM models for studying the toxicity of urban fine PMs applicable for risk assessment.