Antigens of the basement membrane (type-IV collagen and laminin) and the connective tissue (type-III collagen and fibronectin) were studied by immunofluorescence in 16 lymph nodes draining colorectal carcinomas and 6 lymph nodes draining breast carcinomas. A comparison was also made between 7 primary colorectal carcinomas and 9 lymph nodes draining these tumors. Anti-type-IV collagen and anti-laminin rarely stained the basement membrane of metastatic tumors. In contrast, we detected type-IV collagen in the peritumoral stroma, although similar images were rarely seen in primary tumors. When tumoral cells were in the vicinity of lymphoid cells, they were occasionally separated by a barrier stained by the four antisera, or only by antifibronectin and anti-type-III collagen. In other cases no barrier was observed between both types of cells which were in close contact. On the whole the above alterations were more marked in the lymph nodes draining breast carcinomas, in comparison to those draining colorectal carcinomas. Tumor cells were never stained by anti-type-IV collagen or antilaminin serum. Some cells found either in the lymphoid or in the tumor area of metastatic lymph nodes were stained not only by these antisera, but also by a monoclonal antibody against Willebrand Factor, which is a marker of endothelial cells. Thus the labelled cells were characterized as being derived from the capillary wall.