The invention has for its object to provide a porous material capable of relieving the lymphocyte proliferation inhibition in lymphocyte culture and improving the proliferative nature of lymphocytes as well as a method for proliferating lymphocytes and a method for producing lymphocytes each of which utilizes such porous material. The invention relates to a porous material for body fluid treatment for promoting lymphocyte proliferation in lymphocyte culture which contains a high-molecular compound having an angle of contact with water within the range of 40° to 98°； and a porous material for body fluid treatment which comprises activated carbon. It also relates to a treatment device wherein the porous material is used； a method for proliferating lymphocytes； a method for producing mammalian lymphocytes； a method for producing a pharmaceutical composition； an additive body fluid to be added to a culture medium on the occasion of lymphocyte culture； a method for treating a disease against which a therapeutic effect is produced by returning extracorporeally activated mammalian lymphocytes into the body； and the use of activated carbon or a high-molecular compound having an angle of contact with water within the range of 40° to 98° in manufacturing porous materials for body fluid treatment for promoting the lymphocyte proliferation in lymphocyte culture.
