A study was carried out in three metal and nonmetal underground mines, two nongassy and one gassy, to determine if size selective sampling could be used to analyze mineral dust and diesel exhaust aerosols in such mines. Materials mined were shale, soda-ash (497198) and quartzite. The gassy mine (soda-ash) used water scrubbers on diesel equipment, which primarily affected particulate material and not gases. Size differentiated aerosol samples were collected at air intake entries, beltway entries, air return entries and haulage ways. A Micro-Orifice Uniform Deposit Impactor with ten stages from 0.1 to 15 microns was used for size distribution measurements. Results were compared with those from chemical mass balance modeling using dichotomous sampling data. The dichotomous sampler partitioned respirable aerosol into fractions greater or less than 0.7 micron. Mode concentrations of submicron and coarse aerosols were, respectively, 0.6 and 0.7mg/m3 for the shale mine, quartzite mine. For each of the mines, diesel exhaust predominated in the submicron aerosol, with levels of 92, 94 and 95%, respectively. Less than 20 to 40% of coarse aerosols was contributed by diesel sources, the lowest level occurring in the gassy mine. Modal and chemical mass balance analyses gave similar results for amounts of coarse particle contamination of submicron aerosols. These ranged from less than 2 to 5.6%. The authors conclude that size selective sampling may not be ideal for measuring diesel aerosol in metal and nonmetal mines because of coarse fraction contributions by diesel aerosols, and that carbon specific methods should provide higher accuracy.