Strong phenotype. Stage 10 oocytes produced by homozygous females contain fewer and smaller proteinaceous yolk spheres than oocytes produced by wild-type females. These abnormal yolk spheres do contain some yolk. Mature egg chambers (stages 13 and 14) are collapsed within the ovaries. Hemizygous yl^262b/Df(1)g or yl^262b/Df(1)KA9 females have a similar phenotype. The hemolymph of homozygous or hemizygous (yl^262b/Df(1)KA9) females contains a much higher level of vitellogenin than the hemolymph of wild-type females. Electron dense material, which contains vitellogenin, is seen in the interfollicular spaces of homozygous egg chambers. This material is also seen between the completed vitelline membrane and the plasma membrane of the oocyte in older egg chambers. Homozygous and hemizygous stage 10 oocytes have less than 10% of the wild-type number of coated pits and vesicles. The level of vitellogenin in the adult hemolymph of yl⁹/yl^262b females is intermediate between that of wild-type and yl^262b homozygotes. yl⁹/yl^262b stage 10 oocytes have approximately 50% of the wild-type number of coated pits and vesicles.