An identical translocation between the long arm of chromosome no. 1 and the short arm of chromosome no. 15 was found in two unrelated patients with refractory anaemia type I, according to the FAB classification of myelodysplastic syndromes. In the first patient the typical translocation was associated with anomalies commonly found in preleukaemic states, i.e. a 5q- and a 20q- chromosome. Furthermore, in both patients the long arm of chromosome no. 1 was trisomic. Cytogenetic follow-up in the second patient demonstrated a proliferative advantage of the cells bearing a t(1;15) translocation over the cells with trisomy 8 as well as over normal cells. This karyotypic evolution, however, was not accompanied by a transformation of the haematological disorder into acute leukaemia.