Aurora kinase B (AURK B) is a chromosomal passenger protein that is essential for a number of processes during mitosis. Its activity is regulated by association with two other passenger proteins, INCENP and Survivin, and by phosphorylation on Thr 232. In this study, we have examined expression and phosphorylation (Thr-232) of Aurora kinase B during meiotic maturation of pig oocytes in correlation with histone H3 phosphorylation and chromosome condensation. We show that histone H3 phosphorylation on Ser-10, but not on Ser-28, correlates with progressive chromosome condensation during oocyte maturation; Ser- 10 phosphorylation starts around the time of the breakdown of the nuclear envelope, with the maximal activity in metaphase I, while Ser-28 phosphorylation does not significantly change in maturing oocytes. Treatment of oocytes with 50 uM Butyrolactone I (BL-I), an inhibitor of cyclindependent kinases, or cycloheximide (10ug/ml), inhibitor of proteosynthesis, results in a block of oocytes in the germinal vesicle (GV) stage, when nuclear membrane remains intact, however, condensed chromosome fibers or highly condensed chromosome bivalents can be seen in the nucleoplasm of BL-I- or cycloheximide-treated oocytes, respectively. In such treated oocytes no or only a very weak activity of Aurora kinase B, as well as phosphorylation of histone H3 on Ser-10 can be detected after 27 hours of treatment, whereas phosphorylation on Ser- 28 is not influenced. These results suggest that Aurora kinase B activity and Ser-10 phosphorylation of histone H3 are not required for chromosome condensation in pig oocytes, but might be required for further processing of chromosomes during meiosis.