The photolysis of 9,10-anthraquinone (AQ), 2-methyl- and 2,3-dimethyl-AQ was studied in air-saturated acetonitrile–water in the presence of various donors: formate, ascorbic acid, alcohols, e.g. 2-propanol or methanol, and amines, e.g. ethylenediaminetetraacetate (EDTA). The photoreaction is initiated by H-atom or electron transfer from the donor to the AQ triplet state. The conversion of oxygen into hydrogen peroxide occurs via the superoxide radical and its conjugate acid. The quantum yield of oxygen uptake (Φ_−O2) increases with increasing donor concentration. Φ_−O2 = 0.3–0.6 in the presence of 1 M 2-propanol and 3–10 mM ascorbic acid or EDTA. The properties of the quinone and donor radicals involved and the pH and concentration dependences of Φ_−O2 are described.