A few color..variegated blades appeared in the blades regenerated from the MNNG..treated protoplasts of Porphyra yezoensis Ueda. They consisted of the wild..type and color..mutated cells which spottedly scattered. The monospores released from these spottedly variegated blades, developed into single..colored blades ( variants and the wild..type one) and the spottedly variegated blades, which were very similar to the mother blade. From the single..colored variants, three mutant strains were obtained. They showed green, light yellow orange and dull red orange in color, and were designated as yel , och and bus, respectively. The mutant strains were stable in color in both gametophytic blade and conchocelis phases. In the two phases, each mutant strain showed characterist ic differences in the in vivo absorption spectra, and had different contents of major photosynthetic pigments ( chlorophyll .., phycoerythrin and phycocyanin) as compared with the wild..type and with each other. By crossing the mutant with the w ild..type, it was found that the color phenotypes of yel and och resulted from only a single recessive mutation respectively . The mutated gene associating with the color in yel or och is respectively calculated to be 11. 5 or 15. 8 centimorgans from the chromosome.. s cent somere.