This Bureau of Mines report summarizes an investigation of the amount of respirable dust adhering to the surfaces of seven run-of- face broken bituminous coals. The number of respirable-size (0.9 To 10 micrometers) particles adhering to the run-of-face coal ranged from 1011 to 1012 particles per pound of coal and was approximately inversely proportional to the mean lump size of the coal sample. Otherwise it did not vary significantly with the coal seam, mining method, or winning machine. Based on these results, about 16 pounds of ordinary run-of-face broken coal would have enough respirable- size adhering dust to contaminate 1 million cubic feet of air up to the 2 mg/m3 level, if this adhering dust should become airborne. Although brief studies here suggest that a negligible amount of new respirable dust is formed owing to fracture of the broken coal during dropping, dislodging of old adhering particles during secondary handling operations is a potentially dangerous source of airborne respirable dust.