Mutations of the Ki-ras oncogene were analysed by the mutant-allele-specific amplification (MASA) method in pancreatic and colorectal tumour tissues, and T-cell responses against mutated Ki-ras-derived peptides were measured by [3H]thymidine incorporation and IFN-γ production assays. The gene discussed is KRAS; the disease is colorectal neoplasm.