Positive correlations of the magnetic y component of the IMF with those of both the magnetotail lobes and plasma sheet show a By component pervading the quiet magnetotail with enhanced strength near the neutral sheet (z=0). A model constructed using linear solutions to the Grad-Shafranov equation for two-dimensional tail equilibria explains these and related observations in terms of MHD equilibrium theory. We conclude that the enhanced By values must be an essential part of the quiet magnetotail and do not result from a simple intrusion of the IMF. The By field consists of a constant background component plus a nonuniform field existing only in the plasma sheet, where it is dependent on the plasma parameter &bgr; and the strength of the magnetic Bz component. By is strongest at the neutral sheet and decreases monotonically in ¿z direction, reaching a constant tail lobe value at the plasma sheet boundaries. Field lines are tilted about the tail axis with the angle of ascent in the y--z plane being greatest at z=0. This is also the region of greatest field line rotation in the x--y plane, insuring that magnetic reversal always occurs near the neutral sheet. The maximum change in field direction between tail lobes is less than 180¿ with field lines most closely aligned with the tail axis at the plasma sheet boundaries. The presence of a significant positive By component produces currents, including field-aligned currents, that flow through the equatorial plane and toward and away from earth in the northern and southern halves of the plasma sheet, respectively. A negative By component produces currents circulating in the opposite sense. The strength and location of maxima in current flowing along the tail axis depend strongly on the ratio [By(z=0)/By (lobes)>, growing and moving closer to the plasma sheet boudaries as this ratio increases. ¿ American Geophysical Union 1987