Silver staining of proteins separated by electrophoresis in the thin layer of polyacrylamide gel can be quantitatively measured when the results are statistically treated. In the mathematical model, the reduction of protein-bound silver ions (crucial silver staining step) is considered to be autocatalytic. According to the model, the reaction rate strongly depends on the stability constant of silver complexes with functional groups of protein amino acids; and the shape of the calibration curve is determined by the ratio of concentration of silver-binding side chain groups to the reciprocal value of the stability constant. The complex shape of the curves can be explained the combination of autocatalysis and saturation. High sensitivity of this reaction to experimental conditions, contribution of complexes with different stability constants to the intensity of protein band staining, and optical effects are analyzed.