We examined the efficacy of bendamustine in 15 pretreated patients (12 men, 3 women, median age 69 years) with acute myeloid leukaemia (AML) or myelodysplastic syndromes (MDS) 3 AML, 5 sAML, 5 CMML II, 1 RAEB II. Patients belonged to the following cytogenetic groups: 3 complex abnormal karyotypes, 7 normal karyotypes, 1 case with 20q- as sole anomaly and 4 single aberrations. The patients received in median two cycles of bendamustine (range 1-5) with a dose of 100 mg/m(2) at Day 1 + 2 (repeated after 28 days). Nine of 15 patients had no side effects of the treatment, six patients suffered from vomiting and epigastric pain as adverse effects of bendamustine. According to the IWG criteria, no complete remission or reduction of transfusions frequency have been observed. Three patients showed no response, one patient with AML died due to progressive disease. In 11 of 12 patients with initial leukocytosis (median 68,975 microl(-1), range 24,000-149,000 microl(-1)), a significant reduction of leukocytosis was achieved with bendamustine with a median duration of 4 weeks. In summary, treatment with bendamustine in patients with high-risk MDS or sAML with leukocytosis can result in a significant reduction of leukocytes, but fails to achieve hematological responses or improvement of transfusions dependency.