The homotypic homophilic cell-cell adhesion molecule E-cadherin is crucial in the organization and maintenance of most epithelia. The expression of E-cadherin was studied immunohistochemically in various human colorectal tumours. Therefore we stained 1 tubular adenoma with low grade dysplasia, 18 adenocarcinomas with different histologic degrees of differentiation and invasion, and 1 metastasis using a modified peroxidase-anti-peroxidase technique. In the adenoma as well as in all well differentiated adenocarcinomas we found E-cadherin immunopositivity at the cell membrane of almost all cancer cells. The immunopositivity of E-cadherin was clearly weaker and sometimes even absent in isolated neoplastic cells and glands of less differentiated adenocarcinomas. The moderately differentiated adenocarcinomas showed an intermediate staining pattern. These findings are in line with experimental evidence that downregulation of E-cadherin favours invasion, eventually leading to metastasis.