Galectin-3, a beta-galactoside-binding lectin, has been implicated in many human malignancies, but has seldom been studied in human gonads and gonadal tumors. The aim of our study was to investigate galectin-3 mRNA and protein expression in normal ovaries and testes as well as in a variety of 51 gonadal sex cord stromal and germ cell tumors, and two testicular seminomatous and non-seminomatous cell lines, using either real-time PCR or immunohistochemistry. In human testes, galectin-3 is specifically expressed in mature Sertoli cells and Leydig cells, and is absent from fetal and pre-pubertal testes, suggesting a hormone-dependence of this gene. In human ovaries, galectin-3 is absent from granulosa cells, as well as from granulosa cell and Sertoli-Leydig cell tumors, and is not a useful marker in distinguishing granulosa cell from Sertoli-Leydig cell tumors. In testicular tumorigenesis, galectin-3 has a dual function according to the histological type of tumors and their hormone dependency. In malignant testicular Sertoli cell tumors, the expression of galectin-3 is down-regulated while, in benign Leydig cell tumors, this expression is maintained, indicating the possible implication of this gene in the development of more aggressive testicular sex cord stromal tumors. In contrast to sex cord stromal tumors, galectin-3 expression is up-regulated in testicular germ cell tumors. By real-time PCR, we demonstrated a significant elevation of the galectin-3 mRNA level in non-seminomatous testicular germ cell tumors and cell line as compared to normal testes and seminomas (p=0.0432 and p=0.0247, respectively), indicating the possible role of this gene in the non-seminomatous differentiation of germ cell tumors.