Antibodies against the p53 protein were measured with a sandwich-type enzyme-linked immunosorbent assay in blood samples preoperatively collected from 30 patients with ovarian cancer and 30 patients with endometrial cancer. Anti-p53 antibodies were detected in 33.3% of patients with ovarian cancer, comprising 22.2% of the 9 patients with stage I-II disease, 30.8% of the 13 patients with stage III disease, and 50.0% of the 8 patients with stage IV disease. Anti-p53 antibodies were found in none of the 4 patients with well differentiated tumors and in 38.5% of the 26 patients with moderately or poorly differentiated tumors. Among the 21 patients with stage III-IV disease, a complete clinical response to front-line platinum-based chemotherapy was obtained by 46.2% of the 13 patients without anti-p53 antibodies and 25.0% of the 8 patients with anti-p53 antibodies. Antibodies against the p53 protein were detected in only 6.7% of patients with endometrial cancer. The low incidence of anti-p53 antibodies in patients with endometrial cancer seems to suggest that the serum assay of these autoantibodies has a limited clinical relevance in the management of this malignancy. On the other hand in patients with ovarian cancer the incidence of serum anti-p53 antibodies is relatively high, and, moreover, it seems to increase with tumor stage and grade and seems to be associated with a lower response rate to chemotherapy. However, the small number of patients did not allow us to obtain statistically significant differences.