The methods of induced cell fusion are very useful procedures in reproductive and developmental biology. They are used to answer basic questions associated with cell-cycle regulation in mammalian oocytes and embryos (1 ,2 ), to produce tetraploid embryos (3 ), and of particular interest, these procedures are central to the construction of clones, i.e., by allowing nuclear transplantation in mammals (seeChapter 26 ; 4 ,5 ). Various techniques can be used for the induction of fusion. The most commonly used in mammalian embryology are the techniques of Sendai virus-induced fusion, polyethylene glycol (PEG)-induced fusion, and the presently widely used technique of electrofusion (6 ,7 ).
