This is a protocol from: Brussaard, C. P. D., J. P. Payet, C. Winter, and M. G. Weinbauer. 2010. Chapter 11: Quantification of aquatic viruses by flow cytometry. Manual of Aquatic Viral Ecology. Waco, TX:American Society of Limnology and Oceanography. doi:10.4319/mave.2010.978-0-9845591-0-7Please see the published manuscript for additional information.