Comparative genomic hybridization was applied to map DNA gains and losses in 39 invasive ductal breast carcinomas. Frequent abnormalities included gains on chromosomal regions 1q, 8q, 11q12-13, 16p, 19, 20q and X as well as frequent losses on 1p, 5q, 6q, 9p, 11q, 13q and 16q. Furthermore, frequent losses on 4q (20 cases) and 21q (14 cases) were found for the first time in this tumour type. High copy number amplifications were observed at 8q12-24, 11q11-13 and 20q13-ter. Highly differentiated tumours were associated with gains on 1q and 11q12-13 along with losses on 1p21-22, 4q, 13q, 11q21-ter. Undifferentiated breast carcinomas were characterized by additional DNA imbalances, i.e. deletions of 5q13-23, all of chromosome 9, the centromeric part of chromosome 13 including band 13q14 and the overrepresentation of chromosome X. We speculate that these changes are associated with tumour progression of invasive ductal breast cancer.