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The edaphic microalga Neochloris oleoabundans (isolated from desert soil) was subjected to a salt-osmotic shock from 0 to 0.6 kmol m-3 NaCl. The effect of the osmotic upshock on the cell composition was determined. The cell dry weight and the lipid, glycerol and soluble amino acids contents remained unchanged during 5 d of osmotic upshock. The protein content increased after 2d of initial osmotic shock, and it appears to be a long-term haloadaptation process of the cells. The most important short-term effects of salt osmotic upshock were a decrease in polysaccharide content of Neochloris oleoabundans cells. Within the first 4h after the initial shock, there was a transfer of carbon units from polysaccharides to sucrose which was independent of photosynthesis. The increase of intracellular concentration of sucrose contributed to cell osmoregulation. [ABSTRACT FROM AUTHOR]