The effect of pH is studied on the equilibrium and kinetics of heavy metal biosorption. A concept of an effective surface capacity is introduced to describe the equilibrium isotherms of metal ion adsorption. That effective surface capacity is controlled by adsorption of protons. The obtained simple theoretical expressions appear to be very efficient in correlating equilibrium isotherms of adsorption of two kinds of heavy metal ions on two kinds of biosorbents. Next, the statistical rate theory is applied to develop the related expressions for adsorption kinetics. These expressions appear to be very efficient in correlating kinetic isotherms measured at various pH values.