Carbonic anhydrase IX is a transmembrane protein involved in maintaining a low pericellular pH through its reversible conversion of carbon dioxide and water into carbonic acid (Pastorek et al, 1994; Opavsky et al, 1996), and has been shown to maintain survival of breast tumour cells under hypoxic conditions (Potter and Harris, 2003). The gene discussed is CA9; the disease is breast neoplasm.