Bovine oocytes treated using various combinations of 5 muM ionomycin (Ion), 10 microg/ml cycloheximide (CHX) and 5 microg/ml cytochalsin B (CCB) were evaluated to determine developmental rates and ploidy status. The groups were comprised of metaphase II oocytes exposed to Ion for 5 min (Group 1); Ion treatment followed by CHX for 5 hr (Group 2); Ion treatment followed by CHX/CCB for 1 hr and CHX for 4 hr (Group 3); Ion treatment followed by CHX/CCB for 3 hr and CHX for 2 hr (Group 4); and Ion treatment followed by CHX/CCB for 5 hr (Group 5). Group 5 exhibited significantly (P<0.05) lower rates of second polar body (PB) extrusion and higher rates of cleavage and blastocyst development. At 8 hr after Ion treatment, the eggs in groups 2, 3 and 5 were divided into 2 subgroups based on the presence or absence of the second PB and were assessed for cleavage rate and ploidy at the two-cell stage. The cleavage rates did not differ among the activation treatments or between the presence and absence of the second PB in all groups. The diploid rate was significantly (P<0.05) higher in group 5 than in groups 2 and 3. However, the diploid rate in blastocyst-stage parthenotes did not differ among groups 2, 3 and 5. Consequently, oocyte activation by CHX/CCB for 5 hr after Ion treatment could enhance diploid parthenogenetic development in bovine.