Haspin is a protein kinase that regulates chromosome and spindle function during mitosis and meiosis. Haspin expression is detected in fetal liver, skin, kidney, small intestine and in all proliferating cells. Haspin phosphorylates H3 thr3 (H3T3ph) in human cell lines and depletion of Haspin by RNA interference reveals that Haspin is required for H3 thr3 phosphorylation in mitotic cells. Phosphorylation of H3T3ph by Haspin is necessary for chromosomal passenger complex (CPC) accumulation at centromeres. H3T3ph then positions the CPC at centromeres to regulate selected targets of Aurora B during mitosis.