Abnormalities in the p53 gene were studied in a series of cell lines of human squamous-cell carcinoma of the head and neck (SCCHN) and in tumor tissues. Restriction-fragment-length polymorphism (RFLP), quantitative hybridization and immunochemical analysis of mutant p53 proteins were combined to detect and characterize 3 different phases in the p53 gene alteration: mutation (in 9/9 cases), 17p13 deletion (9/10 cases) and amplification of the non-deleted allele (9/31 cases). In SCCHN, deletion of the p53 gene was nearly always accompanied by mutation, only one cell line studied having mutation without deletion. Alterations in the p53 gene are common in SCCHN, and involve a series of genetic events which occur in sequence during tumor progression.