The p53 gene encodes a phosphoprotein which binds DNA. Many types of tumors contain mutant p53 genes, but the effects of these mutations on the intrinsic properties of p53 are largely unknown. In the present study, we tested the effect of p53 mutations on DNA-binding. Each of 15 different mutant p53 gene products derived from human tumors or mouse transformants bound calf thymus DNA more weakly than did wild-type products. A significant subset of mutant proteins were also found to be underphosphorylated compared to the wild-type protein when produced in a reticulocyte lysate system, but this did not appear to explain the pattern of alterations of DNA-binding. The tested mutations were dispersed over several regions of the p53 gene and included representatives of all four of the evolutionarily conserved domains that are the known 'hot spots' for p53 mutation. The results suggest common pathways by which these various mutations affect the normal function of p53.