Karyotyping with fluorescence in situ hybridization (FISH) is reported in two rare cases of AML-M2 FAB. In the first case FISH analysis confirmed the presence of a t(7;11)(p15:p15) translocation in a complex karyotype that also showed an unbalanced translocation involving the other chromosome 7, a rare rearrangement between chromosomes 9 and 20, and four or five copies of a small marker derived from chromosome 9. In the second case whole chromosome painting with probes for chromosomes 8, 14, and 21 revealed the presence of a masked t(8;21) translocation in which one chromosome 14 was involved in a newly discovered rearrangement, i.e., t(8;14;21)(q22-q24;q11;q22). Moreover , double color FISH using ETO-CDR P1 probe and a cosmid for the 5' part of AML-1 on chromosome 21 showed a two color signal on the 8q-, suggesting a recombination between ETO and AML 1. Molecular cytogenetics overcomes limitation of chromosome banding in the interpretation of complex rearrangements.