HARRIS1 first achieved the introduction of a chick erythrocyte nucleus into other nucleated mammalian cells, without any detectable incorporation of chick erythrocyte cytoplasma, using inactivated Sendai virus. Since then chick erythrocyte nuclei have provided a way of investigating the genetic regulation of nuclear synthetic activities in the presence of a genetically disparate cytoplasm and nucleus2,3. Similar studies with nuclei from other mammalian cells have been presented, however, by the lack of a method for obtaining nuclei suitable for introduction into another type of cells.