The Sox-gene family represents an ancient group of transcription factors involved in numerous developmental processes and sex determination in vertebrates. SOX proteins are characterized by a conserved high mobility group (HMG)-box domain, which is responsible for DNA binding and bending. We studied Sox genes in sturgeon, one of the most primitive groups of fishes characterized by a high chromosome number. Male and female genomes were screened for Sox genes using highly degenerate primers that amplified a broad range of HMG boxes. A total of 102 clones, representing 22 different sequences coding for 8 Sox genes, was detected and classified according to their orthologues. Sox2, Sox3, Sox4, Sox9, Sox11, Sox17, Sox19, and Sox21 were found in sturgeon; these genes represent Sox groups B, C, E, and F. In a phylogenetic analysis (neighbor-joining, maximum likelihood, maximum parsimony), these genes clustered with their mouse orthologues. In the case of Sox4, Sox17, and Sox21, we found evidence of gene duplication.