New data on isotopic composition (oxygen-18, deuterium, tritium) of natural waters and ground ice in the Laptev Sea region are presented. The wide spread of modern atmospheric water (younger than 1952) in the upper part of permafrost has been determined. The part of rainwater and snowmelt in the recent ground ice feed is considered. The differences in isotopic composition of the Holocene ice wedges and their recent ice veins reflect well the changes of climatic condition. © A.Yu. Dereviagin, A.B. Chizhov, H. Meyer, 2003.