To study the complex and non identified host causes of summer mortality in C. gigas, divergent selection criteria based upon summer survival have been applied to produce resistant (R) and susceptible (S) oysterfamilies(Samain et al., 2007). A previous analysis by suppression-subtractive hybridization has characterized 46 differentially-expressedcDNAsbetween R and S families(Huvet et al., 2004). The present study reports the screening, using nylon array, of the 46 oyster SSHcDNAsfrom R and S selected families. Among the few differentially expressed genes characterized between R and S samples, one encodes a Transforming-Growth-Factor-β-related (TGFβ) protein. Members of the TGFβsuperfamily are critical growth factors regulating a variety ofimportant processes. We report the characterization and the spatio-temporal expression of oyster-gonadal-TGFβ-like (og-TGFβ-like), a TGFβsuperfamily member specifically expressed in the gonad of the cupped oyster,C. gigas.