Leptin gene expression in white (WAT) and brown adipose tissue (BAT) of the Djungarian hamster (Phodopus sungorus) was analyzed during seasonal acclimatization. Leptin gene expression in WAT was markedly reduced during winter, independent of changes in environmental temperature. Exposure to artificial short photoperiod also decreased leptin gene expression in WATas well as in BAT. Although specific leptin gene expression was lower in BAT, total depot expression was as high as in WAT depots, due to higher RNA content of BAT. Our results indicate that there is significant leptin synthesis in brown fat and that leptin might be involved in photoperiod mediated seasonal adaptations of mammals independent of food deprivation or overfeeding.