In a study of the local immunity in the urinary tract, we have reported on the urinary Immunoglobulin level in normal controls and the localization of In a study of the local immunity in the urinary tract, we have reported on the urinary Immunoglobulin level in normal controls and the localization of urinary Secretory IgA in the urinary tract, using Enzyme-linked Immunosorbent Assay (E. L. I. S. A.) method as a detective method and Enzyme-antibody technique for the study of its localization on tissue. In this study, we observed the urinary SIgA level in various urological diseases and its changes in the course of diseases.The summary of conclusion obtained were as follows:1) The values of SIgA in 147 cases suffering from urological diseases were very high in the cured stage of acute cystitis and neurogenic bladder, especially at the stage of combination of urinary tract infection compared with 34-normal controls. But in acute pyelonephritis its values were very low. In the urological tumors, SIgA values were normal at the stage with tumor, but they decreased after operation, especially in bladder cancer its values were one-fifth of the stage before operation. In urolithiasis, the values of SIgA were very low regardless of presence of stone or not.2) The relation between the values of SIgA and the course of diseases was studied. In 17 acute lower urinary tract infections, most cases revealed high values of SIgA at the infectious stage. The ratio of SIgA at the infectious and cured stage were divided into two groups, one was less than 10 times and another was about 1, 000 times. But this difference was not related to either the infecting organism, the duration to the consultation or cure from onset. SIgA was not reactive in 2 acute upper urinary tract infections. In 10 infections of 8 cases of chronic urinary tract infections, SIgA was highly reactive at the lower one, but even in pyelonephritis its values were revealed about 10 times larger than those in the non-infected stage. The days needed from the onset of infection to the peak of SIgA values were longer than that from the peak to return, and reinfection due to the same organism and the second reaction of SIgA was observed, therefore it was thought to be a lack of immune memory at the urinary tract. In some cases, the normalization of the values of SIgA preceded the disappearance of the urinary tract infection, SIgA was thought to be used as the marker of infection. The values of SIgA observed in one case of renal cell carcinoma were about 1.8mg/day before operation, and revealed high response after embolic infarction of renal artery and nephrectomy. But at 4 days after operation its value was suddenly decreased to 0.5mg/day. At present, 1 year after surgery, it was 0.8mg/day.3) The localization of SIgA on the tissues were studied by the indirect method of Enzymeantibody technique. The tissues studied were obtained from 3 patients with renal cell carcinoma, one with vesical cancer and one with testicular tumor. In renal cell carcinoma, SIgA was recognized at tumor cell cytoplasma and invaded lymphocytes as well as the normal tubular cells. SIgA was strongly localized in papillary tumor cell cytoplasma in vesical cancer. But in testicular tumor SIgA was not found. We thought that, in the urological epithelial tumors, SIgA was secreted from the tumor cell itself or the normal epithelial cell was to be highly reactive against tumor antigens.