Exons 5 to 8 of the p53 gene were examined for mutations in 60 patients with B-cell acute lymphoblastic leukemia (ALL), including 50 cases of precursor-B-cell ALL, nine cases of Burkitt (L3) ALL and one case of atypical ALL with surface immunoglobulins and t(8:14) translocation but L2 morphology. Karyotype was available in all patients. DNA was analyzed by polymerase chain reaction, single strand conformation polymorphism analysis, and nucleotide sequencing. Three patients showed point mutations in exons 7 or 8, including two of the nine patients with Burkitt ALL and one of the 50 patients with precursor-B-cell ALL. These findings suggest that p53 gene mutations are rare in precursor-B-cell ALL but may be more frequent in Burkitt ALL. In the three patients with p53 mutations, however, the relevance of those mutations to the development or progression of leukemia remained uncertain.