The uranyl-alizarin fluorine blue chelate complex shows an absorption peak at 560 nm, 30 nm higher than that of any other single metal complex of the reagent. The complex shows, at pH 4.5, a conditional stability constant of 2.3 × 106litres mole−1and molar absorptivity of 4100 litres mole−1cm−1. Study of the feasibility of using this reaction for the photometric determination of Uo2+2in both one and two liquid phase systems reveals serious interference from other metal ions.