SummaryStarved cultures of Dendryphiella salina were transferred to defined liquid media containing different carbon sources. Mannitol was accumulated in the mycelium in all except arabitol media. By contrast, the rapidly utilized carbon sources gave high to moderate yields of arabitol whereas, with mannitol or carbon sources that were less readily assimilated, there was little or no increase in the level of pentitol.Variation of the nitrogen source in media containing glucose had a significant effect on the accumulation of arabitol but not of mannitol. The results indicate that the quantity of arabitol synthesized is related to the activity of the pentose‐phosphate pathway which in turn is influenced by the form of nitrogen supplied to the fungus.The activities of certain enzymes were determined and these are discussed in relation to Polyol synthesis.