A detailed study is presented on the use of an easily accessible probe (the europium-tetracycline 3:1 complex; referred to as Eu3Tc) for determination of hydrogen peroxide (HP). Eu3Tc undergoes a 15-fold increase in luminescence intensity on exposure to an excess of HP. Data are given on the time dependence of the reaction, on the pH dependence of the absorption and emission spectra of both the probe and its complex with HP, and on the effect of stoichiometry between Eu3+ and Tc on selectivity and signal change. HP can be quantified in aqueous solution of pH 6.9 over a 2-400 mu M concentration range with a limit of detection of 960 nM. The assay is validated using standard additions, and mean recoveries are found to be between 97.0 and 101.8%. Species that interfere in concentrations below 1 mM include phosphate, copper(II), fluoride and citrate. The addition of detergents causes the response curves towards HP to shift to higher HP concentrations. The method is critically assessed with respect to other common optical methods for determination of HP.