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Whole blood and 1% erythrocyte suspensions were treated with crystalline silica (quartz DQ12, Min-U-Sil5) at concentrations of 0.5, 1, 2, and 5 mg/ml. Quartz DQ12 and Min-U-Sil5 revealed a strong dose-dependent hemolytic activity in the 1% erythrocyte suspension reaching nearly total hemolysis (>80%) at the highest tested concentration of 5 mg/ml. This effect may be ascribed to surface reactivity by silanol groups. In contrast, using whole blood cultures the tested silica dusts caused no or only minor hemolytic activity (<4%). The mechanism by which the hemolytic activity is prevented in whole blood cultures can be attributed to a number of factors such as the presence of metal binding proteins and free radical scavenger, antioxidant mechanisms and to coating of the silica surface by proteins, antibodies and complement. In contrast to separated erythrocytes whole blood represents an independent physiological compartment with functions of host defence and regulatory functions against cell damaging effects produced by oxidative stress. [ABSTRACT FROM AUTHOR]