It was shown that expansion of porcine cumulus did not depend on oocyte-secreted factor(s), and it is therefore presumed that porcine CEEF may not be produced exclusively by the oocyte. In this experiment, we used mouse oocytectomized complexes (OOX), which were incapable of CEEF production, to assess the secretion of CEEF by evacuated zona, oocytes of different quality and somatic cells in the porcine follicles. The results showed that: (ⅰ) Evacuated zonae from both porcine and mouse oocytes did not produce CEEF. (ⅱ) Porcine oocytes of A, B and C types from 3 - 6 mm follicles were not significantly different in both production and activity of CEEF. (ⅲ) Both porcine OOX from 3 - 6 mm follicles and granulose cells from < 1 mm follicles secreted CEEF in a large quantity, independent of gonadotropins; mural granulose cells from 3-6 mm follicles, however, produced neglectable amount of CEEF. (ⅳ) The follicular fluid from 3-6 mm porcine follicles contained CEEF activity that was concentration-dependent, and thus it enabled cumulus expansion in 60% mouse OOX when used at 10% of concentration, but the expansion rate of mouse OOX decreased to 9% when the concentration was increased to 50%. (ⅴ) Mouse OOX cultured in porcine CEEF-containing M199 expanded only in the presence of gonadotropins, suggesting that the activity of porcine CEEF is hormone-de- pendent.