Exposures to diesel particulate in underground mining often exceed existing standards. A known carcinogen, diesel emissions have also been linked to a broad range of respiratory and cardiovascular health effects, both acute and chronic. Biodiesel blends are being employed to reduce these exposures, yet there was no information on whether this increases, decreases or fails to change the toxicity to miners of equipment emissions. Some studies suggest a greater toxicity from biodiesel use. This study helped determine the health consequences of the use of biodiesel fuel blends in the underground mining setting. Using a cross-over experimental design alternating use of diesel and 50% biodiesel/diesel blend (B50) fuels, mining and mineral engineering students operated a load-haul-dump vehicle in an underground mine will be monitored for exposure to contaminants and health effects. Respirable dust, elemental carbon, black carbon, nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO), aldehydes, and polycyclic aromatic hydrocarbons (PAHs) were sampled from the mine to determine exposure with the use of each fuel type. Spirometry, symptoms, sputum, blood, urine, exhaled breath, ultrasonography, and other sample types were collected on all subjects pre- and post-exposure to track the health effects of each fuel type. The paired differences in pre- and post-exposure biomarkers of effect were then compared for exposures to diesel and B50 biodiesel. Project work was funded by an NIH grant.