The authors observe, by means of two single Langmuir probes that the scrape-off layer of FT (Frascati Tokamak) is modified during the lower hybrid (2.45 GHz) heating experiments. The modifications are completely different according to whether the plasma line average density is under or above the threshold density nth (Alladio et al., 1982, 1983) for RF-electrons interaction. Some interesting variations with the plasma current Ip and the toroidal field BT are found. The change in the transport properties in the scrape-off due to RF injection is discussed, together with the possibility of taking advantage of the observed phenomena.