The effects of absolute and relative masker duration were investigated using one- and two-tone forward maskers. In the absolute-duration conditions, the duration (D) of a one-component on-frequency (M1; Dm1-alone) or off-frequency (M2; Dm2-alone) masker or the common duration of a two-component masker (Dm1 = Dm2) was varied. Masked threshold increased as duration increased in all three conditions. In the relative-duration conditions, the duration of one masker component was fixed at a relatively long value and the duration of the other component was varied (Dm1 > Dm2 or Dm2 > Dm1). In the Dm1 > Dm2 condition, masked threshold decreased as the duration of Dm2 was increased. In the Dm2 > Dm1 conditions, masked threshold increased and then decreased slightly as the duration of Dm1 was increased. Masked threshold was frequently lower in the M1+M2 than in the M1-alone conditions, indicating psychophysical suppression. Further, masked threshold in the Dm2 > Dm1 condition was always higher than in the corresponding absolute-duration condition (Dm1 = Dm2) having the same M1 duration, indicating masker enhancement. A two-stage neural model was proposed to account for these forward-masking data.