Role of hydrogen peroxide (H2O2) in the induction of cytotoxicity by ascorbic acid derivatives was investigated. Ascorbic acid derivatives which produced radicals (sodium 5,6-benzylidene-L-ascorbate (SBA), sodium-L-ascorbate, D-isoascorbic acid) dose-dependently reduced the viable cell number of human squamous carcinoma (HSC-2, HSC-4, NA), human salivary gland tumor (HSG) and human promyelocytic leukemia (HL-60) cell lines. Conversely, L-ascorbic acid-2-phosphate magnesium which did not produce radicals, was inactive. This suggests the possible role of the ascorbate radical in apoptosis induction. The cytotoxic activity of SBA was partially reduced by catalase, and the extent of inhibition by catalase was considerably different, depending upon which target cells were used. On the other hand, the cytotoxic activity of sodium ascorbate, isoascorbic acid, hydrogen peroxide and gallic acid was more effectively inhibited by catalase. These data suggest that mechanisms other than H2O2 might be involved in the induction of cytotoxicity by SBA.