Abstract. The MHD activity of plasma configurations with reversed magnetic shear has been investigated on the FTU tokamak. In the presence of pairs of surfaces with the same rational value q D m=n of the safety factor, double-tearing modes are excited which give rise in most cases to bursts of sawtooth-like profile rearrangements. More stable regimes have also been found, in which the activity is dominated by rotating saturated modes. In a particular case with q.0 / 2:8 and qmin 2:5 a discharge without any detectable MHD activity during the current flat-top has been obtained. In high-temperature regimes (Te 8 keV at ne 0:81020 m−3), an irregular activity has been detected near the plasma centre which could be due to the excitation of r...