Alterations of the P53 tumor suppressor gene are present in various human malignancies. P53 mutations have recently been detected in 60% of human T-cell leukemia permanent cell lines. To determine the frequency of P53 mutations in primary T-cell acute lymphoblastic leukemia (T-ALL), a powerful method for the detection of structural alterations of DNA was used, namely, single-strand conformation polymorphism analysis of DNA fragments amplified by the polymerase chain reaction. No point mutation in the P53 gene was shown in any of the 30 T-ALL patients tested. Unlike T-cell leukemia permanent cell lines, P53 mutations are uncommon in T-ALL.