Equivalent point source inversion in the rectangular coordinate system has been widely used to reduce satellite magnetic data collected at different altitudes to a common elevation over small areas. This method is based on the expression of the magnetic anomaly caused by a magnetic dipole. Such an expression derived in a spherical coordinate system by von Frese et al. [1981> is found erroneous. We point out the errors in von Frese et al.'s [1981> formulas and present the correct expression for the magnetic field of a magnetic dipole in a spherical coordinate system. ¿ 1998 American Geophysical Union