The human X-ray repair cross-complementing gene 1 (XRCC1) is highly polymorphic in the cells of human head and neck squamous cell carcinoma lines and in a variety of other human cell lines. We describe six patterns seen in Southern analysis of EcoRI-digested genomic DNA. Levels of XRCC1 mRNA vary in cells of human head and neck cell lines as seen in northern blots. Expression of this gene in cell culture does not correlate with radiobiological parameters, clinical outcome, or the DNA restriction fragment length polymorphisms.