A subset of genetic alterations distinguishes two groups of colon cancers. In the first group instability of microsatellite loci due to a defective DNA mismatch repair system is observed. The second group is characterized by recurrent losses of chromosome regions, frequently associated with hyperploidization. We have developed a technique which enables a fine description of allelic losses in this second group of tumours. The typing of 278 loci in 47 hyperploid colon cancers has provided information for an average of 160 loci per tumour. The high frequency of allelic losses on chromosomes 17, 18 and 5 was confirmed thus validating our methodological approach. Several additional chromosome segments were observed lost in over 40% of the cases, suggesting that tumour suppressor genes may map within these regions. Further technical development should contribute to the identification of these genes.