A 81-year-old man was diagnosed as multiple myeloma and had received melphalan for 6 years. After that, he developed acute myeloid leukemia (AML) with monosomy 7 and minor bcr/abl transcripts. Fluorescence in situ hybridization identified no detectable level of bcr/abl rearrangement. During chemotherapy for AML, minor bcr/abl transcripts disappeared and instead major bcr/abl transcripts emerged. He died of pneumonia 3 months later. At that time, neither minor nor major bcr/abl transcripts were seen. These observations suggest that certain therapy related leukemia may be susceptible to generate very small clones with bcr/abl rearrangements.