The theory of filtration efficiency and filter impedance in axially ordered magnetic filters in conditions of laminar flow is described. The now profile of the suspension that flows axially along the longitudinally ordered wires is determined by the Kuwabara-Happel cell model. Expressions for both filter impedance and filtration efficiency are obtained. In general, they are different from those predicted by previous filtration theories in ideal flow conditions. The derived theoretical formulas are simplified so they can be used easily in engineering applications. The results are compared with the experimental ones presented in the literature, and it is seen that they are consistent with each other.