The effects of estrogen and androgens on Vg gene expression were examined in primary hepatocyte culture and livers of the immature male trout. Specific primers of Vg cDNA were designed with already reported Vg gene nucleotide sequences. PCR product was sequenced and verified with Vg cDNA of rainbow trout. Total RNA was extracted from the cultured hepatocytes and livers of steroid-treated rainbow trout and then it was analyzed by reverse transcriptase- polymerase chain reaction (RT-PCR) analysis. The Vg mRNA and Vg protein synthesis were increased in rainbow trout in vivo and in vitro with E$_2$ and methyltestosterone (MT) There were dose and time-related effects of E$_2$ and MT on vitellogesis. Androgens such as progesterone androsterone and testosterone also stimulated Vg mRNA expression in vitro. The results show that androgens as well as E$_2$ can induce expression of Vg mRNA in trout in vivo and in vitro.