A field trial was conducted at an underground gold mine to evaluate diesel fuel derived from soybean oil (soy-methyl-esters or "boidiesel") as an alternative to commercial, low-sulphur, number 2 diesel fuel (D2). A 2.7 m(3), 18-ton load-haul-dump (IHD) unit powered by a naturally aspirated, indirect injection (pre-chamber), 100 kW diesel engine was used as the test vehicle. The LHD was equipped with a diesel oxidation catalyst. The IHD operated satisfactorily on the biodiesel fuel Operators observed a slight decrease in power and an absence of black smoke. Diesel particulate matter (DPM) concentrations were monitored for a six-week period while the LHD was operated with either the biodiesel fuel or the D2 fuel. DPM concentrations were measured in the mining section's clean air intake, exhaust and on the LHD. Reduction in DPM emissions was determined from the measured difference in DPM concentrations between the clean air intake and the exhaust. The biodiesel fuel reduced energy specific DPM emissions approximately 75%, from 3.6 +/- 1.8 g/kW-hr to 0.86 +/- 0.27 g/kW-hr. Time-weighted average DPM exposure, measured near the LHD operator, was reduced from 0.67 +/- 0.13 mg/sm(3) to 0.28 +/- 0.12 mg/sm(3), or approximately 58%, when the biodiesel fuel was used.