A procedure using a porous polymer resin as a trapping medium, was developed and verified as a viable means for collecting gas phase hydrocarbons in the diesel fuel (C10 +) range. The method was then used in a series of diesel and gasoline powered passenger car studies aimed at comparing the gas phase with the particle-bound hydrocarbon mutagenic activity. A second objective was to compare the dilute exhaust polymer trapping method with the cold water raw exhaust trapping system.The VW Rabbit diesel studies showed the gas phase activity to be less than 11% that of the particle-bound with the activity relationship depending upon the test cycle.The gasoline studies showed the gaseous hydrocarbon activity to be at or near background level. A comparison of the particle-bound activity from the diesel and gasoline engines showed the gasoline emissions activity, reverents per mile, to be less than 12% that of the diesel emissions. A comparison of the trapping systems, polymer-dilute vs cold water-raw exhaust, showed good comparability with the Rabbit disel study.