The magnetometer observations on the Traid satellite frequently indicated the existence of a steplike level shift in the field component approximately in the magnetic east-west direction near the expected position of the polar cap boundary. Such a field change implies the presence of a net current flowing into or away from the ionosphere in a current layer parallel to the local L shell. The current direction is toward the ionosphere in the morning half of the current layer and away from it in the afternoon half. These current directions are the same as those of the field-aligned currents observed in the polar cap boundary layer by Ogo 5. Hence a substantial part of the filed-aligned currents discussed in this paper is believed to originate in and return to the magnetospheric tail flowing on the high-latitude boundary of the plasma sheet. The effect of the net current is largest in the late afternoon to the evening, with a maximum in the 1500--1800 MLT interval. Statistically, the magnitude of the net current increases with increasing Kp. When it is extrapolated to Kp=0, the magnitude of level shift does not tend to zero. The average current density in the current layer ranges from 4¿10-7 to 4¿10-6 A/m2. No positive identifications can be made of the current carrier. However, the location of the field-aligned current layer discussed here roughly agrees with that of the region of peak electron intensities determined by McDiarmid et al. (1975) from their Isis 2 observations.