Adult male and female zebrafish were exposed to ethinylestradiol (EE2), methyltestosterone (MT), and Flutamid (F) for one week. EE2 and MT elevated the vitellogenin (VTG) levels in males significantly compared to controls, while no changes in VTG levels were observed in females. Brain aromatase activity was increased significantly in females exposed to EE2 and F compared to control, where as no significant changes in the activity was found in males.