In this study, we have performed fluorescence in situ hybridization (FISH) with chromosome-specific DNA painting probes 1, 2, 3, 4, 6, 8, and 12 and centromere-specific DNA probes 7, 10, 12, 17, 18, and X after G-banding on the same metaphase spreads from four patients with malignant hematological disorders to more precisely interpret their complex karyotypes. The findings demonstrated that the application of combined G-banding and FISH can more accurately explain complex karyotypes of hematological malignancies. FISH can detect not only the origin of marker chromosomes, but also the complex rearrangements that cannot be identified by routine banding techniques. This approach is very important to complement the cytogenetic analysis of malignant disorders and to evaluate the role of chromosome change in the development, progression, and prognosis of tumors. Am. J. Hematol. 55:69-76, 1997.