The hemolytic activities of ten types of Chinese coal dust were examined. Samples of anthracite, lean coal, cindery coal, gas coal, candle coal, lignite, weak caking coal, noncaking coal, fat coal, or meagre coal supplied by the Academy of Coal Science of China were incubated with erythrocyte suspensions prepared from male New- Zealand-rabbits at concentrations Of 0 or 10 milligrams per milliliter (mg/ml). The extent of hemolysis was determined. Anthracite, candle coal, or noncaking coal dust at concentrations of 5, 10, 20, or 40mg/ml were incubated with rabbit erythrocytes to assess dose response effects. Fat coal, anthracite, and cindery coal dust induced 26 to 35% hemolysis and were classified as having the highest hemolytic potential. Meagre, candle, weak caking, and gas coal dust caused 16 to 21% hemolysis and were classified as strongly hemolytic. Lignite, noncaking coal, and lean coal induced 10 to 13% hemolysis and were classified as having low hemolytic potential. At doses below 10mg/ml the hemolytic potentials of anthracite, candle coal, and noncaking coal dust were similar. At concentrations of 10mg/ml or higher anthracite dust was the most hemolytic followed by candle coal and noncaking coal, in that order. Logistic regression analysis indicated that most of the variance in the hemolytic data could be explained by the ash and silica (14808607) contents of the dusts. The authors conclude that the hemolytic activity of the coals depends on coal type which in turn is related to geological age. The silica content of a coal is an important factor contributing to its cytotoxicity. The silica content of coals is related to their geological period of formation.