We investigated the photoamination kinetics of 1-hydroxyanthraquinones in a water-acetonitrile mixed solvent by stationary light irradiation. The progression of the reaction under an inert atmosphere demonstrated the existence of additional reaction pathways. The excited triplet state of the base form of the 1-hydroxyanthraquinones was found to be responsible for the additional pathways. On the other hand, the same reaction under air involved an attack of the amine-derived radical species (aminium and amino radicals) on the ground state of the 1-hydroxyanthraquinones. One of the pathways preferentially led to 2-amination, and the other led exclusively to 4-amination. Results also indicate the attainment of an equilibrium state between the aminium and amino radicals. Copyright (C) 2008 John Wiley & Sons, Ltd.