In general three different chronobiological aspects of cure treatment are important: 1. The spontaneous rhythmic changes of the inner preconditions for therapy, 2. the possible influence of the therapeutical stimuli on the spontaneous rhythms, and 3. the time structure of the adaptational response of the organism. The first aspects particularly meets long-term effects. Annual as well as circadian rhythms not only influence the immediate responses to stimuli, but also their adaptive modifications during cure treatment. The efficiency of external synchronizers is not only determined by the stimultating parameters, but preponderantly also by the internal rhythmic change of the responsiveness. The circadian rhythm of the unspecific sympathetic co-activation meets its maximum in the forenoon, when the morning activation normally occurs. Its regular recurrence in 24-hour intervals contributes to the stabilization of the environmental synchronization. Therefore, the exactly repeating morning activation is significant as to the strengthening of the rhythmic system during treatment. Since the synchronizing reaction of the autonomous system depend on the individual responsiveness, individual differences in the synchronizing response result in different phase positions of the circadian system causing morningness or eveningness. Therefore, the circadian phase position can serve as an indicator for the individual reagibility. When influencing the biological rhythms, it must be taken into consideration that there is existing a hierarchically structured spectrum of rhythms. In the long-wave section (annual, daily rhythm) the rhythms are fixed within their frequency through synchronization by the environ-mental order. In the short-wave section there are found internal coordinations of frequency and phase of the different rhythms, reflecting the entire vegetative state. Therefore, coordinative criteria are suitable to serve as indicators of the self-regulation and the vegetative change-over by treatment. In principle the therapeutic reactions exhibit a periodic time structure (reactive periods). Their period durations, however, are not identical with those of the spontaneous rhythms. As among the spontaneous rhythms complexity and unspecificy of the reactive periods increase with period duration. Whereas single therapeutic stimuli are replied to by periods of several hours, in serial or continuous stimulating load during cure treatment predominate circaseptan (about 7 days) reactive periods, indicating an adaptive response of the organism. The ergotropic phases of the underlying periodically progressing vegetative process lead to the well-known cure crisis, whereas the trophotropic phases promote the progress of adaptation and normalization. Individual differences in the therapeutic reaction are characterized by differences in the periodic time structure in the sense of early-or late-reactive patterns. The circaseptan reactive periodicity can be differentiated clearly from the externally synchronized week rhythm. The chronobiological aspects of cure treatment represent an adequateapproach to the neces-sary dynamic consideration of this, in principle adaptively effecting, therapy.