Cancer-associated mutations in the p53 gene often change amino acids in the protein's DNA binding domain. We used three different binding assays specifically gel shift, DNA binding scintillation proximity assay and a streptavidin magnetic bead assay to analyze the DNA binding of the tumor suppressor p53 from 4 human cell lines with different DNA sequences from the mdm2, p21 and cyclin G genes and a mutant form of the cyclin G sequence. Treatment of MCF-7 cells having wild-type p53 with hydrogen peroxide increased the binding of p53 to DNA as detected using all three assays, but to different extents. The p53 proteins from the thyroid cancer cell lines with different p53 mutations (ARO, WRO and NPA) have comparable binding reactions in the three assays, but show different specificities for the sequences. Here we show that multiple different binding assays allow us to generate a more complete picture of the function of DNA transcription factors in diseases such as cancer.