We examined the c-ets1 gene (located at 11q23) in two myelodysplastic syndrome (MDS) patients displaying a chromosome change at band 11q23 to ascertain any association between this oncogene and the chromosome change. Besides the chromosome change at 11q23, the two MDS patients also showed other numerical and structural changes. Bone marrow cells from the first case showed a translocation between chromosomes 11 and 22, t(?;11;22)(?;p11 or q11----q23;q11), resulting in a Ph-like chromosome. Neither a transposition nor a rearrangement of the c-ets1 gene was detected. Bone marrow cells of the second case showed unidentified chromosomal material attached to bands 11q23 and 6q27. Southern blot study, however, revealed that these cells carried an amplified c-ets1 gene associated with the chromosomal rearrangement. In both MDS cases studied, the amount of c-ets1 related message was the same whether amplification of the c-ets1 gene was present or not, and the level of the c-ets1 gene in MDS cells was very low.