The antioxidative properties of two series of new phenolic, amphiphilic compounds were evaluated using the chemiluminescence (CL) method. 2,2'-Azobis (2-amidinopropane) dihydrochloride (AAPH) was used as a source of free radicals, to obtain high and prolonged CL. Three different kinds of buffers (organic and inorganic) were tested. The CL level varied only slightly depending on the buffer but increased significantly with the pH. Twelve newly synthesised compounds were compared with butylated hydroxytoluene (BHT), a commercially used antioxidant. The new antioxidants included two classes of quaternary ammonium salts with a phenol substituent functioning as an antioxidant. The salts were synthesised by quaternarization of pyrrolidine ethyl esters of dihydrocinnamic acid by n-alkoxymethyl bromides (PYA-n) or quaternarization of 2-dimethylaminoethyl esters by n-alkyl bromides (PPA-n). All the tested compounds quenched CL proportionally to their concentrations. In our experimental conditions 8.5 microM BHT quenched 50% of the CL. The PYA and PPA compounds had IC50 two to six times lower than BHT. CL inhibition was proportional to the pH for all antioxidants. The relationships between the structure and activity of the tested compounds are discussed.