Effects of A23187 on estradiol$-17^{eta}$-induced vitellogenin (VTG) induction were electrophore-tically examined in primary hepatocyte cultures in rainbow trout. hepatocytes were predultured for 2 days and then estradiol-$17^{eta}$(E2, $2{ imes}10^{-6}$M) and calcium ionophore (A23187, $10^{-7)$~$10^{-5}$ M) were added to the incubation medium. The hepatocytes were cultured for 7 more days. In addition, effects of A23187 on $E_2$-primed VTG production were investigated for 7 days. The addition of A23187 ($10^{-7)$~$10^{-5}$M) to the incubation medium specifically reduced VTG production by hepatocytes in a concentration-dependent way. The addition of A23187 significantly reduced the rate of $E_2$-primed VTG production to 18% of the control (E2 only) on Day 7. However, $E_2$-primed VTG production was reduced to 47% of the control by withdrawal of $E_2$ from the incubation medium. Therefore, these results suggest that intracellualr sequestered calcium could regulate VTG synthesis at the translational and/or post-translational stage.