The fractions of apoplasmic water of six moss species were estimated by comparison of the osmotic potentials of fully turgid living tissues ( _(s)) and of killed shoots ( _(k)). The values of _(s) were determined by pressure-volume analysis using thermocouple hygrometry, whereas those of _(k) were obtained by cryoscopy using extracts produced from dried materials and taking into consideration the original saturation water content of the shoots. Most of the tissues had _(s) values around-1 to -1.5 MPa and non-osmotic water fractions of roughly 20% of the total water content at full turgor. Quantitative analysis of a number of osmotically active cell constituents showed that about one-third of the osmotic potential resulted from the accumulation of sugars. The total free amino acids accounted for about 15–20% of the osmolality of the cell solution. Malic- and citricacid contents varied much more with species but, in general, both carboxylic acids together contributed nearly 10–20% to the osmotic potential. The contents of inorganic anions such as free chloride and phosphate in mosses were low.