We have previously cloned Dictyostelium discoideum calcineurin A (CNA) and established a purification procedure for the recombinant protein expressed in E. coli strain TG1. Purification of the tag-free protein included ammonium sulfate fractionation and affinity chromatography on matrix-bound bovine CaM [13]. Since a fraction of the recombinant protein was complexed with the bac-terial chaperone, GroEL, and since silver staining of SDS poly-acrylamide gels for analysis of samples of the EGTA eluate from the CaM Sepharose column revealed the presence of a number of additional bacterial protein bands a further purification step, namely anion exchange chromatography on MonoQ, was necessary to separate free CNA from CNA/GroEL complexes as well as from further bacterial proteins of the CaM Sepharose eluate. In this chromatographic step, an 88 kDa protein of bacterial origin, eluting in a sharp symmetrical peak before CNA and the CNA/GroEL com-plexes during NaCl gradient elution, was identified.