Adding the pigments, methylenblue and fuchsin, to the antigens (E(1)-coli) in advance, their effects to increase the agglutination titer have been studied. The results were as follows: 1) The pigment solution must have the optimal concentration. 2) The agglutination shows higher titer when fuchsin is added than the case of methylenblue. 3) The fuchsin added to H-antigen increases the titer remarkably, but the fuchsin added to O-antigen does not work so evidently. 4) Both, the suspensions of living and formalin-treated bacteria have been tested. The agglutination with living bacteria shows higher titer than with formalin treated ones. In the case of formalin treatment, its lower concentration gives relatively higher titer.