This study examines the effects of a barium-based fuel additive on the polycyclic aromatic hydrocarbon (PAH) content and Ames test mutagenic activity of exhaust particulate matter from a diesel engine commonly used in underground mining equipment. The additive, sold for smoke suppression as Lubrizol 565 and containing 20 - 25% barium, was tested at three concentrations in the fuel: 0.75, 1.5 and 3.0 g/liter. A Deutz F6L 912W 6-cylinder, air-cooled, naturally-aspirated, indirect-injection engine was operated on a programmed, light-duty cycle and particulate matter was collected by dilution tunnel sampling using Teflon-coated, glass-fiber filters.At the manufacturer's recommended level of the additive in the fuel, 3.0 g/liter, particulate emissions were elevated 30% for either intake condition (both with p < 0.01). The barium-based fuel additive also produced statistically significant increases (p < 0.05 or 0.01) in both exhaust mutagenicity (i.e., 160%, standard engine air intake condition with 1.5 g/liter) and exhaust PAH concentration (i.e., 60%, restricted intake with 0.75 g/liter and 79%, restricted intake with 1.5 g/liter). These results suggest that the barium additive should not be used for smoke suppression under light-duty operation. Additional studies are needed to evaluate the additive's effects in heavy-duty work cycles.