Concentrations of many elements in natural waters are generally below the detection limits of most instrumental analytical techniques thereby necessitating their preconcentration. Liquid-liquid extraction has been widely used for this purpose. Nonionic type surfactants offer the best alternative to conventional extraction methods. These surfactants have a critical point (a.k.a. cloud point) above which two isotropic phases are well defined: a dilute aqueous phase containing low concentrations of surfactant and a surfactant-rich phase. Any species that binds to the micellar entity in solution can be subsequently extracted into the surfactant-rich phase. We have been developing micelle-mediated extraction, commonly called cloud point extraction (CPE), procedures in conjunction with neutron activation analysis for the simultaneous determination of a number of elements and their species since 1995. We have studied phase diagrams of PONPE-7.5 and -20, and partition coefficients of PAN and TAN. We have developed CPE methods for: (i) Cd, Co, Cu, Mn, Ni and Zn, (ii) Dy, Er, Eu, Gd, Ho, La, Lu, Pr, Sm, Tb, Tm, and Yb; (iii) Cd, Cr, Hg and Zn; (iv) V; (v) Sb; and (vi) As(III) and As(V) species. A preconcentration factor of 60 and detection limits of 0.03-25 µg kg-1 have been achieved.