In this paper, results from helicopter-borne NOPEX-measurements over a boreal forest using a multi-band radar profiler are presented. Comparisons are made between tree-height profiling responses at three different frequency bands (5, 14 and 35 GHz). Values derived from radar profiles are also compared with maximum tree-height, and stem volume per hectare derived from ground-based measurements made in circular plots below the Eight track. The range response of a radar profiler and its relationship to the foliage back-scattering and stem volume is modelled and discussed. (C) 1999 Elsevier Science B.V. All rights reserved.