In 57 convalescence courses after surgery, temperature, pulse rate and complications recorded daily for 24 days were investigated. Complications were synchronized approximately with temperature. The time structure of the temperature proved to be periodical (reactive periods). The approximately 7-day periods (medium waves) predominated, frequently superimposed by short waves (< or = 4-day periods) and long waves (> or = 14-day periods). There was an intermediate band of approximately 10-day periods. The phases were synchronized with the day of operation, mostly with maxima, otherwise with minima. Periods and phases could jump, the periods preferably in integer ratios, the phases approximately 180 degrees. The long waves yielded a steep drop initially and a reascent of the temperature in the approximately 3rd week. As the number of complications was coincident with the temperature, it also dropped quickly after operation but rose again during the 3rd week. Apart from long waves, temperature and complications descended slowly, synchronizing with the medium waves. The reascent time structure is generally associated with a trophotropic type of patient (late reactive), the gradual descent with an ergotropic type (early reactive). As both of them can be recognized preoperatively, the time structure of the late complications expected can be predicted. Besides the long waves the time structure of the complications is related to the medium waves. Therefore a peak of the complications often occurs at the end of the 1st week.