Results of electromagnetic induction (EM) and drill-hole sea ice thickness measurements performed between 1991 and 2001 on first-year and multiyear ice floes in the Laptev Sea and Transpolar Drift are summarized. They show strong interannual variability between 1991 and 1996, with significantly reduced thickness in 1998 and 2001. First results from operation of a helicopter-based EM sensor in 2001 suggest that this is a valuable tool for flexible and accurate thickness surveys.