A new method is proposed for characterization of particulate forms of radium and barium in natural and waste waters. Particulate solids suspended in 1–3 l. of water are first concentrated by membrane filtration or by centrifugation to 20–50 ml of a concentrate which is then filtered through a small-size membrane filter. The solids retained by the filter are successively washed with three selective solvents releasing “loosely bound”, “acid soluble” and “barium sulfate” forms of radium and barium. Compositions and volumes of the selective solvents have been chosen using model experiments and partially checked by analysis of natural samples. Radium and barium “in crystalline detritus” remain on the filter and are determined after an acid digestion of the filter. The principal criteria and selectivity of the method are discussed.