Reduced expression of pro-apoptotic Bcl-2 family proteins has been described in many gastrointestinal cancers, and may play a role in tumourigenesis. The human homologue of the pro-apoptotic Bcl-2 protein, Bfk, is predominantly expressed in tissues of the gastrointestinal tract. In colon, four alternatively spliced isoforms were identified; of which two are pro-apoptotic when overexpressed. In the transition from normal tissue to tumour, pro-apoptotic Bfk isoform expression is substantially reduced in up to 80% of tumours isolated from the human gastrointestinal tract (8/10 colonic tumours and 26/37 of all gastrointestinal tumours) compared to 3/117 tumours from outside the gastrointestinal tract. These data suggest that pro-apoptotic isoforms of Bfk may help to protect against the development of human gastrointestinal malignancy.