Pig early antral follicles (0.5-1.0 mm in diameter) containing oocytes approximately 100 μm in diameter were collected from ovaries. The intact early antral follicles, oocyte-cumulus-granulosa cell complexes (OCGs), and oocyte-cumulus complexes (OCs) dissected from the follicles were embedded in collagen gels, cultured in Waymouth's medium containing 5% fetal calf serum and 0.05 mg/ml sodium pyruvate for 8 days, and the oocyte morphology was examined. During the culture, follicular cells grew out of the complexes and spread into the collagen gels. All of the recovered oocytes had been detached from cumulus cells in the complexes after the culture. Although no significant increase in diameter was observed, 7% of the oocytes showed normal morphology in the cultured follicles, as did 53% in the OCGs and 47% in the OCs. Before culturing, oocytes from early antral follicles had decondensed filamentous chromatin or thicker stringy chromatin distributed throughout the germinal vesicle (GV0 stage). In the cultured follicles, OCGs and OCs, 0% (0/42), 16% (7/43) and 12% (5/43) of the oocytes, respectively, were at the GVI-MI (the first metaphase) stage, and 2% (1/42), 21% (9/43) and 10% (4/43) of the oocytes, respectively, formed female pronuclei. These results suggest that 37% (16/43) and 21% (9/43) of oocytes in OCGs and OCs, respectively, survived the 8-day culture and advanced their meiotic stage.