In a method for the determination of radium in sea water, radium is coprecipitated with calcium carbonate from the sea water and redissolved in dilute hydrochloric acid; it is then isolated by precipitation with barium rhodizonate, followed by separation on an ion exchange column. The radium compound is then dried and ignited on a platinum disk, and its radioactivity is measured with an α-spectrometer. The average recovery of radium from sea water is 94.0 ± 2.0%.