The Bureau of Mines conducted a laboratory study of the measurement of the water and rock dust (rd) contents of synthetic mine-type coal dust (cd) mixtures using a commercial unit for measuring water content and several prototype radiometric units for measuring the rd content. The rd content ranged from 50 to 100 wt pct and the added water (aw) ranged from 0 to 15 wt pct. The total water (tw) content (intrinsic (iw) and aw) of a small dust sample could be readily measured automatically by essentially untrained personnel using a commercial unit. The rd content of a sample containing only iw could readily be measured by moderately trained personnel using several radiometric units. With gamma-ray devices, about 300 g of sample is needed. With the improved beta-ray device, about 25 g of sample is needed. With dry mine dust samples, the estimated rd error range is 0.8 to 2.3 pct for gamma-ray devices and 0.5 to 1.0 pct for beta-ray devices. However, the radiometric measurement of rd content was questionable if the dust mixture also contained aw or if it was uncertain whether the dust mixture contained aw.