Abstract The influence of various buffering ions and NaCl concentrations on the distribution of Chlorella cells of two strains having differing surface and size were studied in an aqueous dextran-polyethylene glycol phase system using the one-step partition and CCD method. As models for these experiments we used an artificial mixture of Chlorella pyrenoidosa A 24 or Chlorella sp. 366 (strains sensitive to the infective lytic agent) and cells of Chlorella vulgaris B. resistant to this agent. The average size of Chlorella pyrenoidosa A 24 cells was 5.3 ± 0.53 μm and of Chlorella vulgaris B. 6.8 ± 0.55 μm. The condition of complete distribution of this algal mixture in 0.01 M sodium and potassium phosphate buffer is fulfilled when the concentration of NaCl is equal to or greater than a critical concentration of 15 mM of NaCl in the first, and 10 mM of NaCl in the second buffer. In buffers containing—COOH groups at pH 7.3 and low molarity a complete separation of mixture components was obtained. The addition of NaCl to maleate- and fumarate-NaOH buffers of pH 7.3 slightly worsened the separation effect which was visualized when decreasing the r max difference value of both algal components on comparison with the separation obtained in a system without NaCl. At pH 6.0 in various buffers containing —COOH groups a complete separation of the algal components of the mixture was observed only when NaCl was absent. The addition of NaCl to some buffers of pH 6.0, e.g. maleate, malonate, and succinate, destroyed completely the successful separation and gave only a common peak of small r max value. The fumarate buffer of pH 6.0, in the absence of NaCl, was an exception and gave only one common peak of small r max value in contrast to its stereo-isomer maleic acid where two peak separation was obtained.