“…This is a signifi cant advancement over earlier MAR techniques based on morphology, general staining, or antibody staining because it allows investigators to answer questions regarding the metabolic state of microbial communities without a priori knowledge of the microbial community of interest, or when morphology and phylogeny may not refl ect well cellular physiology (Fliermans and Schmidt, 1975;Meyer-Reil, 1978;Fuhrman and Azam, 1982;Neihof, 1982, 1984;Andreasen and Nielsen, 1997). The FISH-MAR technique has proven useful for the study of diverse environments including marine and fresh waters and sediments, hot-spring microbial mats, and contaminated aquifer sediments (Lee et al, 1999;Ouverney and Fuhrman, 1999;Otte et al, 1999;Gray et al, 2000;Nübel et al, 2002;Ito et al, 2002;Glaeser and Overmann, 2003;Malmstrom et al, 2004;Villa et al, 2004;Rogers, 2004). This review examines these techniques and describes their application to soils and sediments.…”