Mutations of p53 frequently occur in a wide variety of cancers including lung, breast, gastrointestinal, brain, and hematologic malignancies. These alterations apparently contributed to development of the malignant phenotype. Wilms' tumor is one of the most common solid tumors in childhood. The frequency of p53 alterations in this tumor is unknown. We analyzed 66 Wilms' tumor samples for p53 mutations by single-stand conformational polymorphism (SSCP) following polymerase chain reaction (PCR). Samples with an abnormal SSCP pattern were reamplified and analyzed by direct sequencing method. Mutations of p53 were found in three (5%) of 66 Wilms' tumors within the coding region (exons 2-11), showing that the frequency of p53 mutations was low. Two mutations substituted amino acids residues and one encoded a stop codon. Two of the mutations were located in the mutational hotspots (exons 5 and 6); the other was in exon 10. These data suggest that p53 mutations are infrequent in the development of Wilms' tumors.