Forty patients, with mainly poor risk haematological malignancies, were given the new regimen FLAG, comprising fludarabine, arabinosyl cytosine and G-CSF. Twenty four patients had acute myeloid leukaemia (AML), 8 patients myelodysplastic syndrome (MDS) and a further 8 patients had a variety of other haematological malignancies. The response rates for 19 relapsed and 4 refractory AML patients were 68% and 100% respectively and comparable to those attained using other regimens, although the numbers are small. Of 8 patients with MDS, 7 showed some response with 4 remaining in an improved disease status 5-12 months after FLAG. Follow-up has been too short thus far to provide any survival data in both patient groups. In general, the other smaller group of 8 patients (3 transformed chronic myeloid leukaemia (CML), 3 acute lymphoblastic leukaemia (ALL), 2 granulocytic sarcoma (GS) did poorly with response shown in 1 only. The regimen was well tolerated with 4 procedure-related neutropenic deaths. The neutropenic and thrombocytopenic periods are generally short when compared with those from current protocols. The overall modest toxicity may encourage combination with other anti-leukaemic agents and be of particular use in the aged or heavily pre-treated patients. Preliminary results may favour the setting up of controlled trials to properly evaluate the benefit of FLAG.