1. Erythrocyte nucleus of adult carp was transplanted into enucleated egg of goldfish to test the totipotency of such differentiated cell.2. More than five thousand injections were made. Only 16% went on cleavage. They formed partial blastulae and blastulae. Only less than 1% went on gastrulation, but the completion of gastrulation was varied, from early epiboly to normal fish formation.3. 16 larvae with complete sets of organs were obtained, but gradually their development became abnormal, the body became distorted and edematous, and in 10—15 days they died without feeding ability.4. Three completely normal juvenile fishes have been obtained from such nucleo-cytoplasmic combination. Two of them died of fungus infestion at the age of 2 1/2 months. The remaining one is still alive now. The phenotypic characteristics of these fishes were of hybrid form. They were single tailed, with. elongated body and large scale as carp, and have the habit of jumping, but the form of the head and the absence of barbel were similar to goldfish. The characteristics of carp shown proves the presence of the function of the nucleus introduced.5. From the results presented above, we suggest that the nucleus of such differentiated cell like erythrocyte is still totipotent. The possible cause of such a low percentage of successful transplantation is also discussed. More than five thousand injections were made. Only 16% went on cleavage. They formed partial blastula and blastulae. Only less than 1% went on gastrulation, but the completion of gastrulation was varied, from early epiboly to normal fish formation.3. 16 larvae with complete sets of organs were obtained, but gradually their development has abnormal, the body has distorted and edematous, and in Three completely normal juvenile fishes have been obtained from such nucleo-cytoplasmic combination. Two of them died of fungus infestion at the age of 2 1/2 months. The remaining one is still alive now. The phenotypic characteristics of these fishes were of hybrid form. They were single tailed, with. elongated body and large scale as carp, and have the habit of jumping, but the form of the head and the The characteristics of carp shown proves the presence of the function of the nucleus introduced.5. From the results presented above, we suggest that the nucleus of such differentiated cells like erythrocyte is still totipotent. The possible cause of such a low percentage of successful transplantation is also discussed.