Salinities of three sediment cores have been determined by the Knudsen titration method and an inductive salinometer. Differences in salinity as large as 2 per mille have been found between the two methods for interstitial waters from blue clays, whereas no differences were observed for the waters from coarser calcareous lutite. Decrease in salinity with depth shown by the inductive method for blue clay sediment is due to exchange and adsorption of ions by clay minerals, preferential precipitation of ionic compounds, or some type of diagenesis. Decrease in salinity with depth is associated with decrease in water content and all of these samples contain the greatest percentage of clay-sized particles. Ultrafiltration processes probably have not been active in any of the cores.