Protein phosphatase 2A alpha (PP-2A alpha) in one of the catalytic subunits of PP-2A, which is composed of catalytic and regulatory subunits. In fission yeasts, PP-2A mutants cause mitotic defects and strikingly different cell cycle phenotypes. In rat hepatocellular carcinomas, mRNA expression of PP-2A alpha was increased compared to that of normal hepatocytes. From these studies, PP-2A alpha has been thought to be involved in proliferation, and we expected that PP-2A alpha would decrease in HL-60 cells on dimethyl sulfoxide(DMSO)-induced granulocytic differentiation with decreased growth rate. In this study, we show that PP-2A alpha expression increases in HL-60 cells on DMSO-induced granulocytic differentiation, while PP-1 gamma, which is one of catalytic subunits of protein phosphatase 1, expression did not change significantly. These results suggest that PP-2A alpha may be involved in regulation of differentiation of hematopoietic cells.