Seventy tumors of invasive ductal carcinoma of the breast were examined for p53 alteration by the RT-PCR-SSCP method. Sixty-five samples (92.9%) were investigated in the regions of codons 101-200 and 201-300. In total, 16 samples (24.6%) showed p53 gene alteration. We found that p53 gene alteration showed a correlation with (1) a negative ER status, (2) a negative PgR status, and (3) a high histologic grade (especially numerous mitotic figures) of the tumor. However, we found no correlation between p53 gene alteration and the lymph node status or clinical stage. Thus, p53 gene alteration in breast cancer may occur in highly malignant breast cancer other than advanced clinical stage cancer or node-positive cancer.