Influence of early ambulation after gastrectomy or cholecystectomy on fatigue reaction (Hamasaki's urinary KES and D. O. K. reaction) was studied as an aid of fundamental investigation, for early ambulation. From the study it was found that the fatigability was not increased even in the first week of ambulation, in early ambulation group as compared with control group, and relieve of fatigue was rather faster and better in the former in during second and third weeks after operation.