The objective of this study was the electron microscope examination of the localization of lipid droplets, mitochondria and other intracellular organelles in bovine oocytes and cumulus cells after Cytochalasin B pre-treatment and ultra-centrifugation. Bovine (n = 180) oocyte cumulus complexes on a germinal vesicle stage were treated with 5 micrograms/ml Cytochalasin B at 38.5 degrees C for 10-15 min. They were then centrifuged at 15,800 g and fixed at 39 degrees C immediately after centrifugation in 3% glutaraldehyde with 0.5% formaldehyde for the microscopic examinations. The centrifugal pole of the oocytes was filled with mitochondria. The centripetal part contained lipid granules and vesicles. Cytoplasm of low density was located in the equatorial region. Hyaloplasm with spontaneously formed membrane and non-membrane vacuoles was located in a supra-equatorial zone of the oocytes. In the cumulus cells the lipid vesicles formed one dark mass in the centripetal pole. The nuclei of these cells were deformed and vacuolization of the cytoplasm was noted.