X-ray microscopy has been performed on unlabeled and gold labeled rat sperm nuclei using a tantalum x-ray laser (44.83 angstrom) and an x-ray zone plate lens. Transmission images of nuclei labeled with gold using an antibody to protamine 1 show large clusters of gold as well as individual 400 angstrom gold particles coating the surface of the chromatin. Images of the same nuclei obtained with a scanning x-ray microscope demonstrate that the initial exposure of the sperm nucleus to a photon intensity of 3.0 × 1014 W/cm2 for a duration of 500 ps did not destroy or grossly distort their structure. Other nuclei labeled with an antibody to protamine 2 were partially decondensed during the labeling process and contained large vacuole-like regions. Images were also obtained of unlabeled sperm nuclei. Data obtained from one unlabeled nucleus imaged with both the atomic force and x-ray laser microscopes was used to determine the thickness of the chromatin and estimate the amount of water that must be associated with the DNA-protamine complex in air-dried nuclei. These results suggest that even air-dried sperm nuclei are extensively hydrated and that tightly bound water may comprise as much as one-third of the volume of the dried sperm nucleus.