We compared detection of rubella virus hemagglutination inhibition (HI) antibody and rubella virus-specific immunoglobulin M (IgM) in dried whole blood spotted onto Whatman ifiter paper and serum samples, both of which were obtained from the same subject by venipuncture. Of 1,000 paired serum samples obtained to study HI antibodies, 807 dried blood samples had HI titers identical to those of the corresponding serum samples, and 193 dried blood samples showed 1 dilution difference. Storage of dried blood at room temperature for 28 days did not affect the HI antibodies. In a study of specific IgM by a solid-phase immunosorbent HI test done with blood from healthy subjects and patients with rubella, the result of the presence, positive or negative, of specific IgM from both-blood sample sources corresponded when the dried blood samples were stored at room temperature from 5 h to 38 days. This study demonstrated that the use of Whatman filter paper as a transport medium for blood samples for the determination of rubella virus immunity and the diagnosis of rubella virus infection is possible.