Pancreatic cancer is characterized by an increasing incidence and an extremely poor prognosis. It is resistant to most of the conventional treatment modalities. Histomorphologically, it presents with a strong desmoplastic reaction around cancer cells, and lymphocytes are typically localized as aggregates in the fibrotic interstitial tissue. Using the method of multi-epitope imaging with fluorochrome-tagged specific MoAbs which allows the simultaneous localization and characterization of T cells in tissues, we studied phenotypes and distribution of tumour-infiltrating lymphocytes (TIL) in pancreatic cancer. CD3+ T cells comprised up to 90% of the tumour-infiltrating cells which were either CD4+ or CD8+, most of them being memory cells (CD45RO+). In decreasing order of frequency, T lymphocytes carried the markers for CD45RO, CD18, CD103 and TCRγδ. Very few natural killer cells (CD56+) were observed. Twenty percent of CD8+ were labelled with CD103. These CD8+ CD103+ T cells, analogous to the gut intraepithelial lymphocytes(IEL), were found in the fibrous interstitial tissue. Furthermore, an inverse correlation was found between the expression of CD18, theβ2-integrin, which mediates adhesion of activated lymphocytes, and CD45RO in the CD8+ subset of TIL (P = 0·046). In conclusion, phenotyping of T lymphocytes in pancreatic cancer raises the possibility that pancreatic cancer cells develop several strategies to escape the T cell-induced cytolysis by (i) the aggregation of cytotoxic CD8+ CD103+ T cells in the fibrous tissue distant from the tumour cells, and(ii) the presence of CD18-bearing cells which lack the expression of the activation marker CD45RO.