This study used a dust chamber to test the response of three direct reading dust monitors, GCA MINIRAM PDM-3, Sibata PCD-1, and TSI 8510, to different dust materials having similar size distributions. Total dust concentrations obtained by open face filters were used as standards for comparing total dust concentration readings, while respirable dust concentrations calculated from particle size distribution measured by the MOUDI cascade impactor were used as standards for comparing respirable dust concentration readings. It was found that the GCA MINIRAM PDM-3 was accurate within +10-16% in regard to total dust concentration, independent of dust material. The calibration constant k of the Sibata PCD-1 was close to 6.0 for both quartz and SAE fine dusts and was independent of dust concentrations. However, for carbon particles, k remains nearly constant from 13-16 only when the total dust concentration is greater than 3.0 mg/m3. The TSI 8510 seriously underestimates the concentration of SAE fine dust, and is more accurate for quartz and carbon dusts when respirable dust concentration is less than 6.0 mg/m3. When respirable dust concentration is greater than 6.0 mg/m3, it will also underestimate quartz dust concentration substantially, while it remains accurate for carbon dust.