The suspended matter in sea water has been separated with membrane filters· (down to 0.1 µ A.P.D.); the inorganic fraction, determined by ignition, has been partly analysed. The methods used are briefly described. An appreciable quantity of finely divided claylike material was found, and it is suggested that, by adsorption of organic matter from the water, this may support the bacterial flora. Samples taken regularly from the English Channel show a seasonal variation...