Ku70 and Ku80 proteins are responsible for the repair of DNA double-strand breaks and function as a regulatory subunit of the DNA-dependent protein kinase. In this study we analyzed expression of both genes in malignant melanoma tissue arrays applying in situ hybridization probes produced by our research group and using immunohistochemical analysis. Expression of both genes was down-regulated as melanoma progressed. In situ hybridization demonstrated more Ku70- and Ku80-positive cells than immunohistochemical methods, but the correlation between the two methods was highly significant (P <0.01). We conclude that the in situ hybridization assay for the detection of Ku70 and Ku80 expression used in this study is also suitable for tissue microarray analysis of paraffin-embedded melanoma samples. The laboratory procedure is much more complicated than the immunohistochemical method, however.