The human epithelial mucin MUC1 is over‐expressed in more than 90% of carcinomas of the breast, ovary, and pancreas as well as in some other tumours, making it a potential target for tumour immunotherapy. We have identified several MUC1‐derived peptides mapping outside the variable number tandem repeat region that comply with the peptide‐binding motif for HLA‐A*0201 and that become processed into stable major histocompatibility complex‐peptide complexes as assessed by in vitro assays. In A2/K^b transgenic mice, 3 peptides, namely MUC_79–87 (TLAPATEPA), MUC_167–175 (ALGSTAPPV) and MUC_264–272 (FLSFHISNL) elicit peptide‐specific cytotoxic T lymphocyte (CTL) immunity, which protects these mice against a challenge with MUC1, A2/K^b‐expressing tumour cells. These peptides therefore represent naturally processed MUC1‐derived CTL epitopes that could be used as components in peptide‐based vaccines and for the analysis of anti‐MUC1 CTL responses in A*0201‐positive patients with MUC1‐expressing tumours. © 2001 Wiley‐Liss, Inc.