The complex of chromosomes and nucleoli, constituting the karyosphere with a capsule, was removed micro-surgically from the late oocyte nuclei of Rana temporaria. Lipids of nuclei and of karyosphere were investigated using biochemical and autoradiographical methods in hormone-stimulated maturing oocytes in vitro. Neutral lipids (triglyceride, diglyceride, cholesterol ester) were found in the karyosphere substance by thin-layer chromatography. During oocyte maturation the incorporation of a precursor (3H-glycerol) into triglyceride was seen to increase much more than into lecithin. The autoradiography on the sectioned oocytes showed that the intranuclear level of 3H-glycerol was more densely distributed in the nucleolar zone over the material of a fibrous component of the karyosphere capsule. The level was also detected over the central part of the karyosphere in close proximity to the chromosomes. The involvement of lipids in organization of the complicated intranuclear complex of the karyosphere with a capsule is discussed. It is suggested that lipid accumulation in the area of the karyosphere fibrous component may reflect their functional relation with the oocyte nuclear matrix.