Magnetic disturbance fields at six mid-latitude stations are computed at 5-min intervals for March 17, 18, and 19, 1978. The three-dimensional current system responsible for the fields was determined on the basis of magnetic records from the six International Magnetospheric Study meridian chains of stations above invariant latitude 50¿ through a numerical modeling method developed by Kamide et al. (1981a). Then each ionospheric high-latitude current segment is assumed to be connected to two (upward and downward) field-aligned currents along the dipole field lines and a closure current in the equatorial plane of the magnetosphere. None of the magnetic records from the six mid-latitude stations were used in determining the high-latitude modeling current system. It is shown that the middle-latitude magnetic disturbance fields thus constructed can reproduce fairly well the observed fields (both the H and D components), indicating that the method developed by Kamide et al. (1981a) is fairly reliable. Further, in agreement with earlier studies, the field-aligned current segments have, in general, the largest contribution to both the H and D components in the middle latitude. The differences between the observed and computed magnetic fields are discussed in detail.