Used as single agents, ATRA, G-CSF, and IFN-alpha have shown a moderate benefit in patients with low-risk MDS, with a response rate of 10%. The aim of the present study was to evaluate the efficacy of a combination of these agents. The effect on hemoglobin (Hb), platelets, and absolute neutrophil count (ANC), as well as on transfusion frequency, was examined in 25 patients with MDS (11 RA, four RARS, eight RAEB, two CMML). The median age was 61 years (range 44-81), and the male/female ratio was 14/11. Treatment consisted of ATRA at 25 mg/m2/day p.o. for months 1, 3, 5, 7, 9, and 11, IFN-alpha at 1.5 MIU twice a week s.c. for 52 weeks, and, in patients with initial ANC <500/microl, G-CSF at 100-480 microg daily s.c. according to the degree of ANC. The duration of therapy was scheduled for 12 months. Two patients achieved ongoing CR (+19 months; +16 months), one patient with RA after 3 months and one with CMML after 7 months of treatment. In all patients, the mean ANC increased significantly from 1400+/-200/microl before the start of therapy to 3500+/-600/microl at the end of treatment (p=0.025). In two patients an increase of Hb was observed, and one patient ceased to require transfusions. In an additional patient with RA and 5q-syndrome, the platelet count normalized following administration of ATRA/IFN-alpha, increasing from 89,000/microl to 293,000/microl. The eight RAEB patients were nonresponders. We conclude that therapy with ATRA, IFNalpha, and G-CSF is effective in approximately 35% of low-risk MDS patients (in this study: six of 17) and may induce complete remission in individual cases.