Our observations of TCR-associated signalling molecules and apoptosis markers in TIL obtained from melanoma and colorectal carcinoma metastases support the hypothesis that lymphocytes at the tumour site manifest a high degree of immunosuppression, as shown by absent ɛ chain or p56lck expression, very low ζ chain and Fas expression, and, most importantly, extremely low FasL expression. This evidence concerns the gene FAS and colorectal carcinoma.