A Mono Q HR 5/5 anion-exchange column with a FPLC system was used to separate exogenously expressed calmodulin from endogenous tobacco calmodulins. Transgenic tobacco calmodulins were purified by fractionation with ammonium sulfate, precipitation with sulfuric acid and hydrophobic chromatography on phenyl-Sepharose CL-4B. The purified calmodulins were chromatographed in the FPLC using the column. This method was selected because of the slight differences in the net charge of foreign and endogenous plant calmodulins due to amino acid sequence differences. By this approach, the exogenously expressed calmodulin was isolated from endogenous tobacco calmodulins. The isolated calmodulin was characterized by amino acid composition analysis as well as methylation analysis.