The Bureau of Mines evaluated two real-time light-scattering dust monitors by measuring their response to Pittsburgh seam coal dust and Arizona road dust (ard). Both monitors--the pds-1, a personal dust sensor, and the pcd-1, a digital dust indicator--are made in Japan by sibata scientific ltd. Tests were conducted inside a laboratory aerosol chamber designed to maintain a uniform spatial distribution of the test dust. Pds-1 and pcd-1 measurements of concentrations for each test dust were averaged over 4-h test periods and compared with simultaneous gravimetric measurements. Both dust monitors responded linearly with mass concentration with both coal dust and ard. However, the linear response of the pds-1 differed from that of the pcd-1 for both dusts.