The expression of p53 in 7 dysgerminomas of the ovary was investigated immunohistochemically with the monoclonal antibodies DAKO-p53/Do-7 and Dianova-p53/Do-l. All the tumors exhibited overexpression of p53 protein. Immunoreactive tumor cell nuclei amounted to more than 50% in 2 tumors, 10–50% in 2 tumors, and less than 10% in 3 tumors. No relationship was found between tumor stage and the degree of p53 expression. Overexpression of p53 thus appears to be very common in dysgerminoma, as it is in epithelial ovarian cancer.