Genetic instability due to a DNA mismatch repair deficiency leads to the replication error (RER) phenotype in cancer cells. Certain loci are more susceptible to replication errors than the genomic average. The mapping of such loci is important, because it could indicate chromosomal domains preferentially affected by RER. Here, we report the radiation hybrid mapping of five markers known to be highly sensitive to RER in carcinomas. They were localized in chromosomes 2q34-q36.1, 6p24.3-25.2, 7q22.1-q13.2, 16q23.2-q23.3 and Xq13.1-q21.2 near genes that could be involved in oncogenesis.