Early in this century, trypsin inhibiting activity has already been recognized in patients with acute infection or renal disease. In addition to these, conditions such as coronary thrombosis, surgical operation, artificial fever by heat-killed bacilli, malignancy, leukemia, later stage of normal pregnancy, etc. have been known to cause the elevated excretion of UTI in urine. Typically, maximal excretion of UTI has been observed within one or two days after the onset. It appears that recent studies have overcome the complexity of UTI molecule. Automated measurement of urinary trypsin inhibitor (UTI) in urine sample was carried out by either enzymic or immunologic method. UTI as well as erythrocyte sedimentation rate and C-reactive protein enables us to monitor acute phase response, being confirmed in cases of abdominal surgery.