A new method of neutron activation analysis of rare earths in natural waters is proposed and applied to thermal and superficial waters. Natural waters samples are irradiated in a liquid state, without preconcentration. The rare earths are separated, after irradiation, from interfering elements by stationary phase chromatography and precipitation. Determination are carried out by gamma spectrometry with a germanium (lithium) detector. The method is applied to quantitative analysis of Dy, Eu, Sm, La, in natural waters, thermal or superficial, coming from Massif Central and Pyrénées (France).