The distribution of laminin in the basement membranes of 20 mucinous tumors and 5 metastatic adenocarcinomas to the ovary was studied using immunoperoxidase techniques to check for invasive carcinoma. Lymph nodes with ovarian tumor metastasis were also studied in 2 cases. Nine cases af 11 mucinous tumors of boderline malignancy revealed linear continuous staining for laminin along the basement membranes around the glands. Only 2 cases showed focal distruption in the laminin staining, accompanied by mucus release or inflammation. Laminin expression of mucinous cystadenocarcinomas was variable and similar to those of boderline malignancy, except areas of stromal invasion. Thick and discontinuous staining of the basement membranes were observed in 4 cases of mucinous cystadenocarcinoma; fragmentary staining in 4 cases; and unrecognizable basement membrane staining in the remaining one case. Laminin stainings were campletely negative in 2 cases of metastatic lymph nodes of ovarian cystadenocarcinoma. Krukenberg tumors were all negative for laminin except only one. The cases of metastatic adenocarcinoma from the large intestine to ovary revealed irregular and fragmentary staining related to the histologic differentiation, the cellular atypism of tumor cells, abnormal glandular architecture of the tumor and the degree of inflammatory cell infiltration.