Nonradioactive in situ hybridization (ISH) using biotinylated centromere probes for chromosomes 1, 6, 7, 10, 16, 17, 18, and the X, respectively, was combined with GTG-banding to study cytogenetic changes in two different ovarian cancer cell lines. ISH was performed after GTG-banding on the same metaphase. The use of a low trypsin concentration (0.01%) in the banding procedure was essential for subsequent ISH. This combined approach allows the detection of subtle chromosomal rearrangements and appears to aid the identification of marker chromosomes.