The molecular characterization of a human testicular proteoglycan, the progenitor of a seminal plasma glycosaminoglycan-bearing peptide, was achieved by cDNA cloning. Its protein core encompasses several domains encountered in various proteins associated with adhesion, migration and cell proliferation. An osteonectin-like domain, a Kazal-like sequence and a 46-amino-acid motif around a Cys-Trp-Cys-Val peptide encountered in cell-surface antigens, cell-adhesion molecules and growth-factor-binding proteins are distributed within the testican protein core. Testican is the progenitor of the unique heparan/chondroitin-sulfate-bearing peptide present in human seminal plasma, a feature which might confer additional potentialities to this hybrid proteoglycan.