A Rb-Sr total rock isotope study of an orthogneiss in Simafjell within the Rödingsfjället Nappe Complex (RNC) in Nordland has revealed a system of several sub-isochrons indicating a resetting event at about 380 m.y. (late Calcdonian time). The result also supports a Precambrian origin for the rocks in question. It is suggested that other Rb-Sr regression lines may be interpreted in a similar way, and that sampling procedures strongly affect the outcome of such studies.