TIMP-1 has an important role in the regulation of extracellular matrix remodeling in many diverse reproductive processes, such as ovulation and implantation. In porcine follicles, secretion of TIMP-1 has been suggested to increase following gonadotropin surge (Smith et al. 1994, J. Anim. Sci. 72:1004-1012). Recent studies demonstrated that TIMP-1 is synthesized by porcine oviductal tissue throughout the estrous cycle and early pregnancy (Buhi et al. 1996, Biol. Reprod. 54 Suppl. 1:103). In bovine, the presence of TIMP-1 in culture medium during early embryonic development increased the incidence of in vitro-produced embryos to develop to the blastocyst stage (Satoh et al. 1994, Biol. Reprod. 50:835-844). However, effects of TIMP-1 in oocyte maturation and early embryonic development are not well defined. The present studies were undertaken to determine whether the presence of TIMP-1 during oocyte maturation or after in vitro fertilization enhances early embryonic development of porcine embryos. Oocyte-cumulus complexes (OCC) were aspirated from follicles (3-6 mm in diameter) of slaughterhouse ovaries, and matured in BSA-free NCSU37 supplemented with 10% porcine follicular fluid, 0.6 mM cysteine, 5 mg/ml insulin, 1mM dibutyryl cyclic AMP, 10iu/ml eCG and 10 iu/ml hCG (OMM37) for 20 h. Those OCC were continue a culture in OMM37 without dibutyryl cyclic AMP, eCG and hCG for a further duration of 24 h. Denuded oocytes were co-cultured with spermatozoa (1 10 6 cell/ml) in modified M190 for 6 h and then cultured in NCSU37 supplemented with 5 mg/ml insulin for 6 days. The incidence of cleavage and blastocyst formation was determined at 48 hours and 6 days after insemination, respectively. Various concentration (0, 1.25, 2.50 and 5.00 μg/ml) of purified ovine TIMP-1 was added during the whole duration of early embryonic development (for 6 days, experiment 1) or the second half of oocyte maturation (20-44 h of IVM, experiment 2). Data (mean±SD) from 3 replications were analyzed by ANOVA and Fisher's protected LSD test. In experiment 1, no differences (P>0.05) were observed in the incidence of embryos to cleave (45±3%) and to develop to the blastocyst stage (20±4%). In experiment 2, however, cleavage rates were higher (P<0.05) when TIMP-1 was added to maturation medium at 1.25 (64±5%), 2.50 (57±8%) and 5.00 ug/ml (56±2%) as compared to controls (43±3%). Further, the incidence of embryos to develop to the blastocyst stage was higher (P<0.05) when TIMP-1 was added at 1.25 (34±4%), 2.50 (32±2%) and 5.00 ug/ml (28±1%) as compared to controls (22±5%). In experiment 2, there were no differences (P>0.05) in the incidence (53±4%) of oocytes fertilized normally (on monospermy and male pronuclear formation). These results indicate that the presence of TIMP-1 during the second half of oocyte maturation, not during early embryonic development, enhances the competence of porcine IVM-IVF embryos to develop to the blastocyst stage.