The objective of this investigation was to determine miners' breathing zone concentrations of diesel exhaust components, to investigate any relationships between these concentrations and vehicle type, the presence of emission controls, vehicle usage, and ventilation conditions, and to make recommendations for monitoring and ventilation requirements. Twenty-two metal/nonmetal mines and two coal mines were surveyed. Sampling was done for cox, nox, sox, pna, aldehydes, and particulates. In most mines, concentrations of at least one contaminant exceeded one-half of the standard or threshold limit value. The concentrations of gases are probably sufficiently reduced by a minimum air velocity of 50 fpm. A sufficient reduction of particulate concentrations may require as high as 400 fpm air velocity. Vehicle age, type, or usage appear to have little or no effect on contaminant concentrations. Polynuclear aromatic levels were below detection limits in all but a very few samples. Minimum requirements for routine monitoring should include formaldehyde, cox, and NO2.