Exposure of the alga Kirchneriella lunaris, isolated from desert soil, to a nutrient solution without phosphorus resulted in distinct growth and protein inhibition in relation to control cultures. In addition, P-deficient algae accumulated much smaller amounts of nitrate accompanied with a rise in free amino acids than the control cultures. The cell multiplications, dry matter, total pigments, proteins, and assay of nitrate reductase of Kirchneriella cultures were generally increased, with a rise in the corresponding P-levels of up to 1250 µg dm-3. Above that the parameters again decreased.