THE concept that humic acids (HA) are heteropolycondensates of phenolic substances is now widely accepted1,2. All the humic acids have hydroxyl, methoxy, or carbonyl groups connected with the aromatic parts of the nucleus. Our earlier investigations suggested that oxidation of hydroxyl groups attached to the aromatic ring may be accompanied by chemiluminescence3–5. It seems probable that chemiluminescence by analogy with fluorescence6 may be able to provide information about the physical and chemical properties and the mechanism of oxidation of the humic acid. Furthermore, the emission of radiation in the course of the oxidation of humic acids may have physiological effects, especially if ultra-violet radiation is present. We have undertaken an investigation in order to gain more detailed information on this problem.