A simple cloud point extraction method followed by inductively coupled plasma-optical emission spectrometry (ICP-OES) was developed for simultaneous preconcentration and determination of trace amounts of U(VI), Th(IV), Zr(IV) and Hf(IV) ions in aqueous samples. The metal ions in 50 ml of aqueous solution (containing 0.1 M sodium acetate, pH 6.0) were formed complexes with dibenzoylmethane (DBM). Then, Triton X-114 (0.2%, w/v) was added to the solution. By increasing the temperature of the solution up to 50 degrees C, a phase separation occurred. After centrifugation at 4000 rpm for 6 min, the surfactant-rich phase (sediment phase) was diluted with 1.0 ml of 20:80 (v/v) of methanol/1 M HNO3. The metal ions were then determined using ICP-OES. Finally, the main factors affecting the cloud point extraction were evaluated and optimized. Under optimized conditions, enhancement factors in the range of 37.0-43.6 were obtained. The calibration graphs were linear in the range of 0.5-1500 mu g l(-1) for Th and Zr, 0.5-500 mu g l(-1) for Hf and 2.5-1240 mu g l(-1) for U with correlation coefficients (r(2)) better than 0.9926. The detection limits were between 0.1 and 1.0 mu g l(-1) and the R.S.D. values for seven replicates were lower than 6.1%. (C) 2007 Elsevier B.V. All rights reserved.