The behaviour of a series of stable cyclic aminoxyl radicals in the presence of SDS micelles was studied by EPR spectroscopy. Six different compounds, i.e. two non-phosphorylated and four β-phosphorylated, were investigated. Except in the case of the strongly hydrophilic 3-CP 1, which always remained in the bulk aqueous phase, all the radicals were found to exchange between water and micelles. Their partition coefficients were evaluated from computer simulations of the EPR spectra and in the case of two aminoxyls TOMER-Et 5 and TOMER-Pri 6, the variation of the rate constant with temperature allowed us to estimate the exchange activation energy.