In this letter, the effect of helical anisotropy, induced by torsion strain, on the circular permeability μΦ, of a vanishing negative magnetostrictive CoFeSiB wire is presented. As a function of a dc applied magnetic field, Hdc, μΦ shows an asymmetric behavior dependent on the direction of the applied torsion strain: for counterclockwise torsion angles (-), a monotonous decrease in the μΦ (Hdc) double peak magnetoimpedance response is observed together with a linear increase in the wire’s circular anisotropy field Hk. In contrast, for clockwise torsion angles (+), a gradual suppression of the μΦ (Hdc) maxima was evident, for which a magnetic softening of the wire is assumed. Results are interpreted in terms of a counterbalance/enhancement effect of the wire’s circular anisotropy for + and - torsion angles, respectively. © 2003 American Institute of Physics.