The developmental abilities of porcine oocytes matured and fertilized in vitro were examined in vivo and in vitro. Cumulus-oocyte complexes were cultured in mM199 supplemented with 10% porcine follicular fluid (PFF) and hormonal supplements (PMSG, hCG and estradiol-17 beta) for 20 h and then without hormonal supplements for an additional 20 h. In Experiment 1, oocytes were then co-cultured for 6 h with spermatozoa which had been preincubated with 1% PFF (PFF-treated) or without (control). Oocytes were transferred to oviducts of gilts or cultured in modified Whitten's medium for 5 d. The percentages of oocytes with monospermic penetration (59%, 42/71) and with monospermic penetration and male and female pronuclei (32%, 23/71) were higher (P < 0.01) in the PFF-treated group than in controls (25%, 18/71 and 8%, 6/71, respectively). After 5 d, the percentages of oocytes that developed to the morula or blastocyst stages in vitro and in vivo in the PFF-treated group (10%, 28/288 and 13%, 41/318, respectively) were also higher (P < 0.05) than in controls (2%, 6/284 and 6%, 16/248, respectively). Whereas some oocytes that were matured and fertilized in vitro developed to the blastocyst stage after 5 d in vivo culture (3%, 9/288 in PFF-treated group and 2%, 6/284 in control), no blastocysts were observed after 5 d when oocytes were cultured in vitro. When the progression of in vitro development of porcine oocytes that were matured and fertilized in vitro was examined in Experiment 2, morulae appeared after 72 h of culture, and 3% (3/100) of the oocytes developed to the blastocyst stage after 144 h (6 d) of culture. These results demonstrate that decreasing polyspermic penetration and increasing monospermic male pronuclear formation, as a result of PFF treatment of maturing spermatozoa, improved the developmental ability of porcine oocytes matured and fertilized in vitro. However, development in vitro was delayed by approximately 24 h compared with in vivo development, most of the embryos were blocked at the morula stage.