AbstractBackground and Methods: In an effort to review ultrastructural features of cells in the kidney of a male rat, transmission electron microscopy was used to study ultrathin sections.Results: One light cell in a collecting tubule contained a 2.3‐μm long linear array of electron‐dense asymmetric structures in a granular zone of greater electron density than the general cytoplasm. This inclusion body could be interpreted to consist of a parallel array of 100–150‐nm × 24‐nm electron‐dense rodlets, or a parallel array of 100–150‐nm×67‐nm tubules. The inclusion showed no association with any cell organelle. The origin, chemical nature, frequency of occurrence, and functional significance of this inclusion are unknown.Conclusions: Although this inclusion body somewhat resembles previously described inclusions or granules, the differences in dimensions, frequency, and relation to other cell structures suggest it is a new observation. ©