The following continued adaptation of Hennes et al. (1995) is a result of FLVP assay optimizations for the Vibrio alginolyticus PWH3a-phage P1 phage-host system (PHS) for use with SYBR Green I stain. Novices to microscopy would benefit from reading Wen et al. (2004) for details on preparing and storing slides using SYBR Green I stain. This protocol is a modification of the standard slide preparation techniques for bacteria and viruses in aquatic samples (see Suttle and Fuhrman 2010, this volume).