Eighty-nine cases of primary breast carcinoma were evaluated immunohistochemically for basement membrane laminin and fibronectin (FN). 58 of the cases were also examined by transmission electron microscopy (TEM). Intraductal carcinomas were all positive for laminin and FN and by electron microscopy a continuous BM was found in all of them. Among invasive tumors, immunoreactivity for laminin was expressed in 31% of cases and FN in 66%, whereas TEM revealed BM in only 4 out of 52 (8%) studied cases. Tumors measuring 10 mm or less were more often laminin-positive and FN-negative than larger tumors. There was a tendency for lymph node negative tumors to express laminin more often, but there was no relation between lymph node status and FN. Laminin immunostaining proved to be very useful in identifying vascular invasion. The laminin and FN immunoreactivity showed no significant correlation with overall survival and disease-free survival (DFS) of the breast cancer patients. DFS for cases with laminin positive tumors was 50% and for laminin negative tumors 46.8%. For cases with tumors immunoreactive for FN, DFS was 50%, and for tumors lacking FN 43.5%.