Chlorinity variations have been determined vertically and horizontally in Postglacial clay sediments from the Ancylus and Littorina periods. The analyses were made by fusing the soil samples and by determining the Cl-contents. Comparative analyses were made by a leaching method. The factors influencing the chlorinity of sediments are discussed. The leachhg method gives lower Cl-contents than the fusing method. The vertical chlorinity variations of the sediments do not very well reflect the salinity variations in the Baltic during the period studied, as revealed by investigations of the diatoms of the sediments. Variatiom of the chlorinity within the same stratigraphic layer, with that same original Cl-content, may be due to differences in grain size and content of organic matter. The Cl-content alone of the sediments is not an adequate criterion of the paleosalinity.