We analyzed clinical trials of low dose cytosine arabinoside (LDARA-C) in 324 patients with acute myelogenous leukemia (AML) and 129 patients with myelodysplasia (MDS). Complete and partial remission rates were 31% and 18%, respectively, in patients with AML, and 24% and 27% in patients with MDS. Toxicity was primarily hematologic. Although in vitro data suggested that LDARA-C acts as a differentiating agent, clinical data generally indicate a cytotoxic mechanism. Given the lack of effective therapeutic options in MDS and high risk AML (patients greater than 65 years old, secondary AML), these data are encouraging. LDARA-C warrants further study, comparing continuous infusion with intermittent subcutaneous administration and comparing LDARA-C to conventional dose therapy.