1. The rate of microbial respiration on fine-grained stream sediments was measured at 196 first- to third-order sites in the mid-Atlantic region of the United States. 2. Sample collection took place between April and July in 1993, 1994 and 1995. 3. Study streams were randomly selected from the United States Environmental Protection Agency's (USEPA) River Reach File (RF3) using the sample design developed by USEPAs Environmental Monitoring and Assessment Programme (EMAP). 4. Respiration rate ranged from 0 to 0.622 g O2 g-1 ash-free dry mass (AFDM) h-1, and was significantly correlated with stream temperature, water chemistry and physical habitat. 5. Respiration rate was significantly higher in streams from the Chesapeake drainage area compared to those from the Ohio drainage area, and in streams from the Northern Appalachian Plateau and Uplands and Central Appalachian Valleys ecoregions compared with streams from the Blue Ridge and Central Appalachian Plateau ecoregions. 6. Respiration was not significantly different among stream orders or between years.