Long-period (20--50 s) surface-gravity waves were recorded in the eastern Arctic (83¿N, 10¿E) using tiltmeters deployed on the ice and an acoustical current meter deployed a few meters below the ice during the spring of 1989. The waves caused ice tilt of a few microradians and horizontal velocity of the water just beneath the ice of order 10-4 m s-1. The unprecedented sensitivity of the velocity measurements is the result of a path-averaging technique based on reciprocal transmission along 200-m horizontal paths. The measurements indicate infragravity waves and low-frequency swell penetrate the Arctic Ocean through the Fram Strait and that they are freely propagating and not tied to groups of short waves. It is suggested that these waves could provide a method to measure ice thickness distribution in the Arctic Ocean. ¿American Geophysical Union 1995