When Dendryphiella salina was grown on non-saline media, mannitol and arabitol were the only polyols present in the mycelium. In media made up with sea-water or salinized by high concentrations of salts of potassium, sodium and magnesium, glycerol was also present. When mycelium grown in sea-water was transferred to distilled water, the glycerol content dropped very rapidly to zero. The amounts of mannitol and arabitol also declined. Transfer of similarly grown mycelium to sea-water alone reduced the rate of decline of glycerol, caused little change in the amount of mannitol and induced a rise in that of arabitol. These observations help to explain the absence of glycerol in mycelium in previous studies. The concentration (mol l−1) of solutes within mycelium were determined after 48 h growth in the presence of either sodium chloride, magnesium chloride, sodium sulphate, inositol or betaine at either 0.4 or 0.8 osmol kg−1water. There was a very similar total polyol concentration at each osmolality in the saline media irrespective of the salt, even though there could be different concentrations of individual polyols. With inositol in the medium, the same held if the endogenous concentration of that compound was included in the total. The same did not hold for betaine, in which medium growth was poor. The total polyol concentration increased in all cases with the osmolality of the medium. With respect to the total concentration of solutes present (excluding data for mycelium grown in betaine), polyols were 19 to 33 % of the total, α-amino nitrogen, 11 to 34% and organic acids, 0 to 8 %. These percentages take into account data obtained by 24Na-flux studies, which indicate that, in media containing sodium salts, much of the mycelial content of the cation may be located in the wall.