The objective of this contract is to provide independent surveillance of the health status of rats in the NIA supported, contractor maintained colonies known as the """"""""Aged Hybrid Rat Colonies"""""""". This health monitoring is to provide monitoring which is independent of that provided by the colony contractors for two purposes: 1) confirmation of results reported by the colony contractors, and 2) to serve as a resource for resolution of questionable animal health problems and advise on animal health management practices. The health monitoring to be provided will include gross pathology, histopathology, microbiology, parasitology and serology.