The differential equations governing the eddy-current distribution in the flow field of the electromagnetic blood flowmeter yield two solutions. The first is that of the flow-induced current and the second relates to the ‘quadrature’ current which is caused by time-changing magnetic fields. The quadrature current equations are solved for a flow tube of cylindrical geometry with a transverse uniform cylindrical magnetic field. These results form the basis of a more general solution in which the magnetic field is allowed to vary in the direction of the lumen axis. Experimental results demonstrate the accuracy of the theory developed as a means for describing and calculating the quadrature currents which are the primary cause of baseline drift in electromagnetic flowmeters.