The tumour-associated antigen UK114, isolated from goat liver, belongs to the YER057c/YIL051c/YjgF protein family, which has members in both the prokaryotes and eukaryotes. The crystal structure of a mammalian representative, goat UK114, was determined, revealing a trimeric arrangement in the crystal. It was confirmed by ultracentrifugation that UK114 is a trimer in solution. These results are in agreement with the published structures of homologues from unicellular organisms, but contrast with those reported for the rat homologue of UK114, for which a dimeric quaternary structure was proposed.