Fatigue reaction by the method of D. O. K. was determined on ninety one cases performed major laparotomies, before and after operation for three weeks. Results obtained were as follows. 1) Reaction of D. O. K. determined in uriue, matutinal or preoperative, of various diseases were generally higher than normal, and mostly moderate in the reaction. In the cases with acute inflammation it was significantly elevated with parallel to the extent and severity of inflammation, On non-inflammatory diseases, it was higher in late stage of stomach cancer, bleeding ulcer and intestinal obstruction, successively stomach cancer resected, peptic ulcer with complication of stenosis, cholelithiasis in order. It was lowest and minimum in the cases of uncomplicating ulcer. 2) In the postoperative course, the level of D. O. K was markedly increased in general within one to three days after operation, gradually decreased later until normal on the seventh day, and below normal for two to three weeks until recovery. In the case of stomach cancer resected, the decrease was retarded as compared with that in the case of uncomplicating ulcer and not become normal even after three weeks. The decreasing rate was gradual in the case of acute inflammation, especially in the severe, and not returned to normal even after three weeks. In acute simple appendicitis, though, the level became normal within seven days after operation. 3) In the cases with postoperative complications urinary D. O. K. was increased and showed retarded restoration of the level. 4) From the results obtained above, it was concluded that determination of D. O. K. level in matutinal urine before and after operation was valuable for reading the grade of operative procedure, course of postoperative recovery and the prognosis.