The objectives of this investigation were to determine the amount, size, and deposition of float coal dust generated during the mining and transporting of coal in underground U.S. mining operations. Rock dust distributed by trickle dusters was also sampled. In addition to four belt-transfer points, two continuous and two conventional mining sections were sampled at five mines located in Pennsylvania, West Virginia, Kentucky and Illinois. Float-dust samples were collected on deposition pans; total airborne dust was collected with MSA Model G personal samplers equipped with Unico filter casettes; Andersen cascade impactors provided relative size distributions of the samples. Production, airflow, and waterflow were monitored to examine their effect on dust levels.