Annual records on the abundance of lemmings (Lemmus sibirica and Dicrostonyx torquatus) and the frequency of dens occupied by reproducing arctic fox Alopex lagopus on the Taimyr peninsula, Siberia, are reported for the time period of 1960—2001. A strong correlation was demonstrated between lemming abundance and the frequency of dens occupied by breeding foxes. This finding is supplemented with certain observations of birds on the peninsula, and information on the reproduction biology of lemmings and arctic fox. Since the breeding success of several bird species nesting on the Siberian tundra are much affected by the population interactions of lemmings and arctic fox, base-line data on these mammals are needed for proper evaluation of avian records, including those from southern migration and wintering areas. The time series reported is the longest yet provided on lemming abundance and reproduction of Arctic Fox.