Here we report on the successful reprogramming of nuclei from somatic cells rendered nonviable by heat treatment. Granulosa cells from adult sheep were heated to nonphysiological temperatures (55 degrees C or 75 degrees C) before their nuclei were injected into enucleated metaphase II oocytes. Reprogramming was demonstrated by the capacity of the reconstructed embryos to develop to the blastocyst stage in vitro and into fetuses and viable offspring in suitable foster mothers. To our knowledge, this is the first report of cloned mammalian offspring originating from nonviable cells. In addition, our experiments show that heat-treating donor nuclei destabilizes higher-order features of chromatin (but leaves intact its nucleosomal organization) and results in a high proportion of reconstructed embryos developing to the blastocyst stage and beyond.