A panel of HepG2-derived cell lines (CAT-Tox [L] assay, Xenometrix), harboring stress genes consisting of a sequence for chloramphenicol acetyltransferase (CAT) under the transcriptional regulation from mammalian promoters and response elements, was exposed for 18-24 hr to aqueous suspensions of urban dusts (SRM-1648, SRM-1649, EHC-93) or PM2.5 particles (particulate matter < 2.5 fim). Expression of CAT protein was measured by enzymelinked immunosorbent assay. Induction of the CAT genes was verified with benzo[a]pyrene (CYPlAl, cytochrome P450 1A1 promoter; GSTYa, glutathione transferase subunit Ya promoter; XRE, xenobiotic response element), cadmium sulfate, and copper sulfate (HMTIIa, metallothionein ria promoter; HSP70, heat shock protein 70 promoter). The urban dust suspensions were active on CYPlAl, GSTYa, and XRE cell lines. SRM-1648 and SRM-1649 were twice as potent as EHC-93 per unit mass in inducing the xenobiotic-dependent responses, which correlated with contents in polycyclic aromatic hydrocarbons. These three reference particles, as well as six PM2.5 preparations collected on hivol filters in the Great Lakes basin, were also found to induce HMTIIa and HSP70, the magnitude of the responses correlating closely with the amount of soluble copper in the particulate preparations. The results indicate that bioavailable chemical species in the unfractionated particles can directly and quantitatively induce xenobiotic, metal, and stress-dependent responses in a target cell model, resulting in patterns of gene induction consistent with the chemical compositions of the environmental materials. We propose that cell culture models could be helpful for toxicodynamic inferences in adjunct to environmental monitoring and exposure assessments.