The invention relates to an aqueous solution containing at least one species selected from the group consisting of a 1:1 molar complex of TeO.sub.2 with a moiety of formula (A) and ammonium salts thereof: HO--X--OH (A); where X is an optionally substituted divalent saturated hydrocarbon group containing 2-8 carbon atoms in the chain connecting the two OH groups; and its use for stimulating cells to produce cytokines and for treating mammalian diseases and conditions responsive to increased production of cytokines. The complex may be used also for treating mammalian cancer which is not responsive to increased production of cytokines.