Ultracentrifuging (400,000 g for 4-6 h at 4 degrees C) living wild-type cells of the fission yeast Schizosaccharomyces pombe moves the nucleus towards the ends of the cells but scarcely affects their viability. However, in the long cells produced by growing the mutant cdc2.33 for 4-6 h at the restrictive temperature (36.5 degrees C), ultracentrifuging (as above) gives an intense fluorescence with DAPI in about half of the cytoplasm in about 80% of the cells. This is probably nuclear DNA that has moved into the cytoplasm, both because of the DAPI stain and because it is removed by DNase treatment. These cells ultimately divide and are viable, and we suggest that the extended cytoplasmic DNA returns to the nucleus.