Inherent DNA damage in the form of single strand breaks and alkali labile sites is generated by essential intracellular processes, such as DNA replication and repair. Utilizing the in situ DNA unwinding assay and the comet assay (single cell gel), we have observed high levels of alkali induced DNA strand breaks in cells isolated from mouse kidney tissue homogenate. Kidney cell DNA demonstrated a 7.4 x increase in nucleoid expansion and a 7 x increase in comet length compared to negative control cells (thymocytes and splenocytes) in the two assay systems, comparable to epididymal sperm cells which have previously been demonstrated to contain abundant alkali-labile sites. These results argue for the existence of prevalent alkali-labile sites in kidney cell DNA.