BACKGROUND/AIM: The insulin-like growth factor type 1 receptor (IGF-1R) is overexpressed in myelodysplastic syndrome (MDS) cells, and 765IGF-Methotrexate (IGF-MTX) is a conjugate of methotrexate and a variant of insulin-like growth factor-1 (IGF-1) designed to selectively target cancer cells through binding to IGF-1R. The aim of this study was to determine whether IGF-MTX would be effective to treat MDS. PATIENTS AND METHODS: In this phase I clinical trial, two patients with high grade MDS or oligoblastic acute myeloid leukemia (O-AML) that had failed standard therapy were treated with IGF-MTX. RESULTS: No dose-limiting toxicity was observed. Both patients had stable or improved cell counts and CD34+ myelodysplastic cell counts and exceeded their life expectancy (both alive at 1.9 years despite a life expectancy of less than 6 months). Bone marrow blast counts decreased from 22% to 5% in one patient, and from 17% to 16% in the other. CONCLUSION: In conclusion, IGF-MTX at 0.20 μM equivalents per kg was well tolerated, caused no cytopenia, and produced stable disease and extension of life.