The paper demonstrates that the intensity variation in a magnetic tape passing through a recording gap forms part of a series of unclosed and markedly asymmetrical hysteresis loops. The effect of asymmetry is investigated theoretically and shown to give distinctive properties to the recording and distortion characteristics of unbiased recording. The gap length of the recording head is critical under these conditions and leads to the occurrence of maxima and minima of recorded level and distortion at specific wavelengths. These properties are confirmed by experiment, and the mechanism of recording employing h.f. bias is examined in the light of the findings. It is shown that the number of bias cycles normally available during the time a tape element is in the recording gap is insufficient for hysteresis symmetry to be attained. Various predictions are made concerning the transitions which may be expected in the recording and distortion characteristics as the h.f. bias field is increased from zero to saturation value. These transitions have been demonstrated experimentally, and it is shown that adequate h.f. bias eliminates the asymmetry of the a.f. intensity variation. A symmetrical variation of a.f. intensity results in the recording and distortion characteristics normally observed. The effect of a bias-leakage field outside the recording gap is discussed briefly with reference to the coercivity of the tape material.