Calmodulin, as a major intracellular calcium‐binding protein, regulates many Ca²⁺‐dependent enzymes and plays an important role in a wide spectrum of cellular functions of the eukaryotes. Interaction between calmodulin and human lactoferrin, a 78 kDa protein with antibacterial properties, was found in the presence of Ca²⁺ using (i) a method for the detection of calmodulin binding proteins with biotinylated calmodulin, (ii) affinity chromatography on an agarose—calmodulin column with subsequent detection by an enzyme‐linked immunosorbent assay (ELISA). The binding of calmodulin to lactoferrin blocked the ability of lactoferrin to agglutinate Micrococcus lysodeikticus.