Abstract The cytotoxic and hemolytic potential of coal fly ash derived from a number of thermal power stations in India was investigated on guinea pig macrophages and mammalian erythrocytes respectively. The cytotoxic studies were carried out using graded concentrations of fly ash. Fly ash‐macrophage interaction resulted in increased release of LDH into the supernatant culture medium. Acid dye uptake was enhanced only when the interaction ensued in a serum free milieu. Both the extent of enzyme release and dye uptake were significantly more in quartz exposed cultures than in those exposed to fly ash. In hemolytic assay all fly ash samples produced only a meagre hemolysis of erythrocytes, irrespective of the mammalian species from which the erythrocytes were obtained. Concentrations which produced more than 75 percent hemolysis of quartz exposed erythrocytes produced less than 10 percent hemolysis when erythrocytes were exposed to fly ash. These results reveal a weak membranolytic activity of coal fly ash.