Immunosuppressive substances with molecular weights higher than globulin can be effectively removed by means of double filtration plasmapheresis (DFPP). This paper describes the result of an experiment on the ability of microporous glass bead adsorbent (GBA) to remove immunosuppressive substances with molecular weights lower than albumin, which cannot be removed by DFPP. Sixteen kinds of GBA were tested, each having a different surface charge and pore size. The immunosuppressive activity of serum was measured by means of lymphocyte blastogenesis to phytohemagglutinin. The serum treated with GBA of 100 A in pore size and having a surface coated with-NH(2) showed the highest reduction of the immunosuppressive effect. The decrease in the immunosuppressive effect was observed after an incubation time of as little as 5 minutes and at a serum-absorbent ratio of 20. Regarding the adsorption of immunosuppressive acidic protein, a 43% decrease in the concentration was seen from the initial level of 931ng/ml after incubation in vitro. This adsorbability of the GBA was also observed in an extracorporeal perfusion test. It was revealed that removal of immunosuppressive substances in the low molecular weight fraction is feasible by the use of the GBA. It is supposed that removal of immunosuppressive substances would be more effectively performed by simultaneous use of GBA and DFPP.