We have found a 33 bp minisatellite repeat in the 5'-flanking region of the mutated in colon cancer (MCC) gene at chromosome 5q21. Southern blot experiments demonstrated the locus specificity of the repeat. The number of repeat units varied between 5 and 11 with a heterozygosity of 0.56. The sequence 5'-AGG AGT GTG AAT GGG GCA TAG TGA ATG AGG GGA-3' of the repeat units does not match the consensus sequence of chi-related minisatellites. The minisatellite is not expressed as part of a gene transcription unit. However, it can be used as a tool for the detection of allelic changes at chromosome 5q21 on standard agarose gels.