We describe the clinical, haematological and cytogenetic features of three patients who had acute myelogenous leukaemia (AML) with complex bone marrow karyotypes when first cytogenetically examined. Induction chemotherapy led to remission from the acute leukaemia. However, neither clinically nor morphologically did this remission mean a return to normal haematopoiesis. The two patients who displayed myelodysplastic features before and when AML was diagnosed, again developed myelodysplasia, and the third patient, who had a long history of polycythaemia vera, returned to this myeloproliferative condition. Nor was cytogenetic normalization achieved; instead, abnormal cell clones were found in which all but one of the karyotypic aberrations present at acute leukaemia diagnosis had disappeared. The solitary anomalies that were detected in these reemerging clones must correspond to the primary cytogenetic aberrations of the patients pre-leukaemic diseases. They were del(5) (q11q33) and del(17) (p11) in the two myelodysplastic cases, and der(18)t(9;18) (p11;p11) in the patient with long-standing polycythaemia vera. The other, secondary, aberrations were probably the leukaemogenic changes, and with the eradication or reduction of the subclones containing them, the leukaemic phenotype disappeared. The three cases add cytogenetic evidence to the growing understanding that the remission obtained in some AMLs is actually a return to a preleukaemic, myeloproliferative or myelodysplastic, syndrome.