We have undertaken the cytogenetic monitoring of 39 adult patients treated for de novo acute myeloid leukemia (AML) by intensive chemotherapy. We describe this monitoring in seven patients in continuous complete clinical and morphologic remission (CR) of AML. Although in CR, these patients exhibit the emergence of cytogenetically abnormal clones. Abnormalities observed include monosomy 7, del(20)(q11), partial trisomy 1q, and 6p12-22 rearrangements. They correspond to well-known chromosomal rearrangements commonly found in myelodysplasia (MDS), and myeloproliferative syndromes (MPS), as well as AML. Present as the sole detected chromosomal change, they preceded by months the onset of overt leukemia or MDS. In some cases, the abnormal clone showed a proliferative advantage (some patients exhibited up to 100% of abnormal bone marrow metaphases in subsequent analyses). AML relapse, when it occurred, was associated with a different chromosomal modification. Altogether the question arises, whether the abnormalities pointed out in our study (monosomy 7, del(20)(q11), partial trisomy for the long arm of chromosome 1 (q21qter), 6p12-22 rearrangements), and seen after chemotherapy, mark preleukemic cells or not, and whether they participate indirectly, or not at all in the leukemic process.