SOX proteins contain a conserved HMG-related DNA-binding domain. They fulfil essential functions during the development of animals. Mutations in several SOX genes have been implicated in human diseases, We present here a new set of PCR primers designed to amplify a broad range of SOX HMG-box sequences. These primers facilitated the cloning of several new SOX HMG boxes from human genomic DNA, revealing unexpected complexity of the SOX gene family. (C) 1998 Federation of European Biochemical Societies.