Particulate and sulfate emission characteristics of two catalyzed radial- flow wire-mesh particulate traps are presented. The traps were found to be ineffective for particulate reduction. The first trap was dynamometer tested for 25 consecutive EPA Heavy Duty Diesel Transient Cycles and 40 hours of steady state operation. During steady state testing, particulates were sampled from both the raw and diluted engine exhaust. The total particulate matter was chemically analyzed for sulfate, organic, moisture, and nonextractable fractions. The data indicate significant conversion of fuel sulfur to hygroscopic sulfuric acid. Although solid carbon fraction was reduced, total particulate mass increased. Sulfuric acid condensation presented operational and particulate sampling difficulties. Sampling from the raw exhaust with heated lines showed good sulfur balance between fuel and exhaust contents, but sulfate emission also exceeded the baseline for total particulate matter. Steady state tests with a second trap with a different catalyst formulation produced similar results and no improvement in total particulate emissions.