Abstract Cloud point extraction has been used for the preconcentration of cobalt and nickel, after the formation of a complex with 1-(2-thiazolylazo)-2-naphthol (TAN), and later analysis by flame atomic absorption spectrometry using octylphenoxypolyethoxyethanol (Triton X-114) as surfactant. The chemical variables affecting the separation phase and the viscosity affecting the detection process were optimized. Under the optimum conditions, preconcentration of only 50 ml of sample in the presence of 0.05% Triton X-114 permitted the detection of down to 0.24 μg l −1 cobalt and 0.44 μg l −1 nickel. The enhancement factors were 57 for cobalt and 65 for nickel. The proposed method has been applied to the determination of cobalt and nickel in water samples.