Because the spleen is likely to play a specific role in immunity, we have tried to observe the influence of the abdominal neoplasms on splenic lymphoid tissue as well as the distribution and localization of immunoregulatory cells with a special attention to the marginal zone, using splenectomy specimens in the various kinds of 121 abdominal neoplasm patients. As a control group, twenty-six splenectomy specimens from patients with traumatic rupture were used. In splenic size and weight, there was a statistically meaningful increase in the patients with abdominal neoplasms. Among those patients, the evolving activated immune reaction (EVA) was 60.2%, the early activated immune-reaction (EAA) 39.0%, the mixed evolving activated and granulomatous reaction (MIX) 0.8%, unlike EVA 30.8%, EAA 69.2%, and MIX 0% in the normal control group. The reason for this change may be explained by activated lymphoid tissue in the form of EVA type. In conclusion, the splenic lymphoid tissue in the various kinds of abdominal neoplasms, mostly malignant, revealed the chronic immune activated state characterized by the increased number of prominent germinal centers and distinct marginal zones, the latter of which revealed the positive reaction for L26, IgM and IgG, and negative for IgD, as well as showing increased natural killer and dentritic reticulum cells identified by Leu7 and S-100 protein respectively. Therefore, we could at least find the significance of the immunologic role of the spleen in the case of abdominal neoplasms, mostly from malignancy.