Computer simulation of isotachophoresis of proteins using carrier ampholytes such as Ampholine or Sepaline as the spacers was performed on the basis of the author's theory of steady state electrophoresis. As carrier ampholytes behave as if they were weak acids in anionic isotachophoresis, the simulations were performed on systems composed of five weak acids with similar pK values in the absence or in the presence of up to two protein components. The results could explain those of agarose gel isotachophoresis experiments of proteins using carrier ampholytes as the spacers.