The catalytic subunit of telomerase (hTERT) has recently been proposed as a potential tumour-associated antigen capable of inducing T-cell mediated immunity in cancer patients. Before any attempts at vaccination with hTERT antigens can be made, one should establish if cancer patients possess cytotoxic T-lymphocytes (CTL) that can recognise hTERT epitopes. The T-cell response against two HLA-A2-specific epitopes of hTERT in 37 colorectal cancer patients and 12 normal controls was analysed using an interferon gamma (IFN-gamma) ELISPOT assay. For comparison the response to HLA-A2-restricted epitopes of CEA and influenza A matrix protein was also measured. CTL that recognised either of the two hTERT epitopes studied were found in 7 (19%) of colorectal cancer patients, with 2 (5%) possessing T-cells that recognised both these peptides. Four (11%) colorectal cancer patients had CTL that reacted to the CEA epitope. No relationship between cancer stage and the presence of specific CTL against hTERT or CEA was observed. None of the normal controls possessed T-cells capable of recognising either the hTERT or the CEA epitopes. However, a similar proportion of patients and normal controls had CTL reactive with the influenza A peptide. The results of this study demonstrate that CTL active against hTERT are present in approximately 20% of colorectal cancer patients irrespective of disease stage. Moreover, these cells are functional, able to secrete IFN-gamma when stimulated with the relevant peptide.