A variety of physical and chemical stimuli initiate egg activation events. This study was designed to investigate the rates of pronuclear formation and the cytoskeletal organization of porcine oocytes activated by various stimuli. Oocytes matured for 44–60 hrs were activated by one of the following treatments: double electric pulses (EP, 150 V/mm for 60 µsec, 1 sec apart), ethanol (7% for 5 min), calcium ionophore A23187 (CaA, 50 µM for 2 min), cycloheximide (CHX, 5 µg/ml for 6 hrs), or 6-dimethylaminopurine (DMAP, 2.5 mM for 4 hrs). EP yielded the highest activation rate (97%). CaA and DMAP activated the oocytes in relatively higher proportions than did ethanol and CHX (74 and 83% vs. 55 and 41%, respectively). After CHX and DMAP treatments, egg fragmentation was significantly increased (65 and 82%, respectively) and the polar body emission was restrained. After activation with EP, ethanol or CaA, the pronucleated oocytes possessed a microtubule-rich domain around the pronucleus, which was concomitantly surrounded by microfilaments. In oocytes activated with CHX or DMAP, however, microtubules and microfilaments did not synchronously form a concentrated domain. We suggest that activation with a protein synthesis/phosphorylation inhibitor may have affects on distribution and function of the cytoskeleton of the oocyte different from those elicited by treatments with EP, ethanol or CaA, which result in higher proportions of eggs with the pronucleus restrained in the peripheral ooplasm and greater egg fragmentation.