In this study we have established a system for expression of the catalytic subunit of protein phosphatase type 2A (PP2A) of bovine adrenal medulla in E. colL Expression of PP2A in pQE31 vector, based on use of the phage T5 promoter and two lac operator sequences, produced the enzyme as an insoluble aggregate which constituted up to 30-35% of total cellular protein. Although enzyme activity was not detected, the protein had an Mr of 36 kDa, comparable to that of authentic phosphatase 2A isolated from human red blood cells. Both the recombinant protein and the authentic phosphatase 2A exhibited cross-reactivity with specific antibody against a synthetic peptide cor- responding to PF2A amino acid residues 296-309, The insoluble protein, fused with a 6x His affinity tag was directly applied to a Ni-NTA column for purification by affinity chromatography. Approximately 90% homogeneity was obtained by a single purification and the enzyme was essentially homogeneous after further passage through a gel filtration column. These procedures yielded about 15-20 mg purified PP2A/liter culture,, which will facilitate further renaturation experiments and future studies on structure-function relationships of the enzyme.