By centrifuging monolayers of rat L6 myoblasts adhering to plastic discs in the presence of cytochalasin it is possible to enucleate close to 100% of the cells. The nuclei drawn out of the cells are surrounded by a narrow rim of cytoplasm and an intact plasma membrane and therefore are ‘minicells’ stripped of most of the original cytoplasm. In addition to minicells, the pellet material on the bottom of the centrifuge tubes contains fragments of cytoplasm and occasional intact cells. The number of intact cells can be drastically reduced by precentrifugation of the monolayers prior to enucleation so as to remove loosely attached cells from the plastic discs. Biochemical analysis of minicell pellets show that at least 65–75% of the original cytoplasm is removed during enucleation. Microinterferometric dry mass measurements on individual minicells where free cytoplasmic fragments (without nuclei) can be excluded indicate that at least 80–90% of the cytoplasm is removed. Most of the minicells are impermeable to trypan blue and are able for some time after enucleation to incorporate precursors into nucleic acids and proteins. Under normal tissue culture conditions the minicells fail, however, to regenerate a cytoplasm and to multiply. Instead the minicells undergo a gradual decrease in dry mass and most seem to be dead 36 h after enucleation. The minicells can, however, be rescued by fusion with enucleated cytoplasms and may therefore be used to reconstitute nucleated cells.