Аннотация:In three Far Eastern male forest cats (Prionailurus bengalensis euptilura) and four male domestic cats (Felis catus) with preimplanted (under general anesthesia) loggers, deep subcutaneous back temperature and motor activity were recorded in captive conditions for two months in the fall–winter period. It was found that in fall, at positive daytime temperatures, the circadian rhythm of body temperature is absent in Far Eastern forest cats and weakly expressed in domestic cats. However, it reappears during the period of winter cold in the form of fluctuations, synchronous in all animals, with an amplitude of 3–4°C and acrophase in the middle of the daylight period and a minimum in the middle of the night. For comparison, the recording of the “core” body temperature and activity in two female domestic cats kept in the same season in the laboratoryrevealed no comparable rhythms. It is concluded that the restactivity and deep subcutaneoustemperature circadian biorhythms are not constant characteristics of the body of Far Eastern forestand domestic cats, but can appear, disappear and change radically with changes in ambienttemperature.