Arsenic trioxide (As2O3) induces remission in a high proportion of patients with acute promyelocytic leukaemia (APL) via induction of apoptosis. Preliminary reports suggest that the apoptotic effect of As2O3 is not specific for APL but can also be observed in non-APL acute myeloid leukaemia (AML) cells, although these are less sensitive than APL cells. Ascorbic acid has recently been demonstrated to enhance the apoptotic effect of As2O3. We have therefore evaluated combined As2O3/ascorbic acid treatment in various clinical samples of AML. Our results indicate a significant synergistic effect of As2O3 and ascorbic acid, suggesting a possible future role of As2O3/ascorbic acid combination therapy in patients with AML.