The paper offers a basic investigation of magnetic-fluid sealing. The objectives aimed at quantitative relationships between the parameters of the magnetic circuit, the properties of the fluid, and the resulting Δp capacity of a single or multistage seal. The pole pieces were investigated with the aim of arriving at an optimum configuration which would yield maximum sealing capacity for a given total space. It is shown that lines of constant intensity represent to a good approximation also lines of constant pressure and thus potential interfaces for the magnetic fluid; and that maximum sealing capacity is obtained when tooth width is twice and intertooth spacing three times the clearance.Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in San Francisco, California, August 18–21, 1980.