In this paper, the author intended to analize the mechanism of acceleration in the growth of Brown-Pearce Tumor (BPT) after splenectomy, described in my previous paper. Considering the intimate relationship between spleen and reticuloendothelial system (RES), author followed up the function of RES in BPT bearing rabbits and examined the influences of splenectomy upon them. The phagocytability of RES detemined by use of Adler-Reimann's Congored Test and the ability of antibody formation was estimated from the value of haemoagglutinin (HA), formed after the intravenous injection of 5% physiologic saline solution of healthy O-type human red blood cells, of 3cc per 1 Kg of body weight, into rabbit, 3 or 5 days after the transplantation. The result revealed as follows; 1) The phagocytability of rabbit was not disturbed by the implantation of BPT into the testicle and by continuous localized growth of tumor tissue, but in accordance with the beginning stadium of remote metastasis, an impairement of this function appeared gradually. 2) It was the noticeable fact that the marked deterioration of HA formation in BPT bearing rabbit occurred from such early stage of transplantation as the tumor was hardly palpable in the testicle. And that this phenomen was not due to the tissue transplantation was proved by the experimental results showing no decrease in HA formation after the implantation of the liver homogenate into a testicle of normal rabbit. 3) The fluctuation of increase in serum γ-globulin level accompanied with HA formation went parallel with values of HA in seruem. This suggested that the lowering of haemoagglutination did not depend upon the inhibition by such substance in serum as mucoprotein, but upon the poor formation of HA itself. 4) In BPT bearing rabbit, although the phagocytability was not influence by splenectomy, but the deterioration of HA formation ability showed further increase in its grade by splenectomy. 5) From the results described above, the author presumed that this marked deterioration of HA formation ability in BPT bearing rabbit was specific for the existence of growing tumor tissue, and was due not to the exhaustion of the function of RES, but probably to the preceding formation of antibody against the tumor tissue in RES, aud, in this point of view, splenectomy would give an influence upon the tumor growth as a sequela of an influence upon the fuction of RES.