The kinetics and mechanism of the adsorption of the surface layer proteins of Lysinibacillus sphaericus CCM2177 on gold depend on the charging conditions of the electrochemical double layer and the addition of Ca(2+) ions. The electrical and mass charging was monitored by an in situ electrochemical quartz microbalance. Adsorption and monolayer formation of the protein molecules occur in the positive potential region where solvated anions form the electrochemical double layer. The crystalline character of the surface layer was diagnosed by an atomic force microscope. Negative of the point of zero charge, multilayer island structures were found.