The human MSH-2 gene product is a member of a highly conserved family of proteins involved in post-replication mismatch repair. Germline mutations in this gene have been implicated in hereditary non-polyposis colorectal cancer (HNPCC). Alterations in the coding region of the hMSH-2 gene result in a mutator phenotype with marked instability of microsatellite sequences, indicative of a deficiency in DNA repair. We have previously shown that a region of high homology between MutS proteins of different species containing a nucleotide binding domain, is sufficient to bind DNA containing specific mismatched residues. In order to determine the minimal domain of hMSH-2 necessary for binding mismatch-containing oligonucleotides, deletion analysis of the C-terminal region was performed. We have constructed a 5' and 3' deletion series, expressed each deletion as a bacterial fusion protein and assessed it for ATPase activity and its ability to identify mismatch containing DNA. Here we demonstrate that a 585 bp fragment encoding 195 amino acids within the C-terminal domain of hMSH-2 is sufficient to bind to DNA containing mismatches.