Free-running human circadian rhythms in Svalbard.

The body temperature, activity-rest time, electrolytes of urine samples and mood was measured in two persons a 19 day period under continuous light conditions in the arctic (vicinity of Ny Alesund, Svalbard-Spitsbergen). For temperature recording a new thermoprobe and a portable printer was used. Possible week Zeitgeber of the 24 hour day did not synchronize the circadian system, since circadian rhythms of about 26 hours were found. These results open up the possibility to study effects of drugs on the circadian system of humans under Svalbard conditions.