Differential production and uptake of two forms of vitellogenin (VgA/B and VgC) was verified in serum and oocytes, respectively, of Japanese medaka (Oryzias latipes). The ratio of the two types of Vg (VgA/B:VgC) in the serum of females varied with reproductive stage (range ~2:1-8:1). In males exposed to waterborne E2 for various durations or at various dosages, the induced Vg ratios were fairly constant (~2.4:1-3.4:1) except that VgC alone was detected after a very short (2 h) exposure to E2. An antiserum against VgC (a-VgC) immunostained yolk granules in pre-vitellogenic oocytes when no immunoreactivity was found by staining with a-VgA/B. Both antisera stained yolk globules in vitellogenic oocytes. The reproductive phase-specific differences between plasma levels of VgA/B and VgC likely reflect different rates of their hepatic synthesis and uptake by oocytes.