Mechanisms mediating vascular calcification remain incompletely understood. Nanometer scale objects hypothesized to be a type of bacteria (nanobacteria) are associated with calcified geological specimens, human kidney stones, and psammona bodies in ovarian cancer. Experiments were designed to evaluate human vascular tissue for the presence of similar nanometer-scale objects. Calcified human aneurysms (n = 8), carotid plaques (n = 2), femoral arterial plaques (n = 2), and cardiac valves (n = 2) and noncalcified aneurysms from patients with bicuspid aortic valve disease (n = 2) were collected as surgical waste from the Heart Hospital of Austin, Austin, Texas, and Mayo Clinic, Rochester, Minnesota. Whole mounts or adjacent sections from each specimen were examined by electron microscopy, stained for calcium phosphate, or stained with a commercially available antibody (8D10). Filtered (0.2 microm) homogenates of aneurysms were cultured and costained with 8D10 antibody followed by PicoGreen to detect DNA or incubated with [3H]uridine. Staining for calcium phosphate was heterogeneously distributed within all calcified tissues. Immunological staining with 8D10 was also heterogeneously distributed in areas with and without calcium phosphate. Analysis of areas with positive immunostaining identified spheres ranging in size from 30 to 100 nm with a spectral pattern of calcium and phosphorus (high-energy dispersive spectroscopy). Nanosized particles cultured from calcified but not from noncalcified aneurysms were recognized by a DNA-specific dye and incorporated radiolabeled uridine, and, after decalcification, they appeared via electron microscopy to contain cell walls. Therefore, nanometer-scale particles similar to those described as nanobacteria isolated from geological specimens and human kidney stones can be visualized in and cultured from calcified human cardiovascular tissue.