The effect of osmotic stabilizers on protoplast formation of yellow/white color mutants of Chlorella ellipsoidea was studied. The UF-1 strain, one of the mutants, had the same growth rate as the parent C. ellipsoidea at 4.02 muE/m(2)/s and no reversion to normal cells at 0-26.8 muE/m(2)/s. Therefore, protoplast formation from UF-l was carried out, and it was found that the yield of protoplasts was 93% in the medium containing 1.0 M NaCl as an osmotic stabilizer.