Three sensitive and selective new alternatives for fluorometric determination of cerium(III) are described in this study. Ce(III) is highly fluorescent in sodium pyrophosphate, sodium trimetaphosphate, and sodium tetrametaphosphate solutions. For these reagents, the maximum excitation/emission wavelengths are 300/350, 297/340, and 299/352 nm, respectively. Maximum fluorescence intensities are obtained by irradiating Ce(III) dissolved in 0.033 g L-1 sodium pyrophosphate, 41.4 g L-1 sodium trimetaphosphate, and 0.96 g L-1 sodium letrametaphosphate at room temperature. The fluorescence intensities are linear over the range 0.001-30,0.001-75, and 0.001-70 mu g ml(-1). The detection limits are calculated as 9.5 x 10(-3), 1.1/10(-3), and 3.8 x 10(-3) mu g ml(-1) Ce(III), respectively. The relative standard deviations for 15/0.05 mu g ml(-1) Ce(III) are 1.1/1.2, 1/1.1, and 1.2/1.3%, respectively. Quenching effects of other lanthanides and some inorganic anions were investigated. The Methods have been applied to rare earth mixtures with a good accuracy.