The ultimate objective of this study was to examine the viral flora of waters from estuaries, inland ponds and streams of Rhode Island. However, prior to carrying out field examination, it was necessary to evaluate under controlled laboratory conditions these methods currently available for sampling, concentration and isolation of viruses with a view to selecting the most effective method or designing a method which would simplify sampling and improve recovery. The methods evaluated included the gauze pad technique, adsorption and elution from chemical flocs, combined flocculation and centrifugation, sonnication, and finally adsorption and elution from magnetic iron ore. The gauze pad was found to be inefficient for recovering virus from fresh water but its efficiency was enhanced slightly by the presence of inorganic salts in water, e.g., sea water. Combined flocculation and centrifugation improved viral recovery, but showed selectivity in the viruses recovered. The best results were obtained by adsorbing virus onto magnetic iron oxide followed by elution with blood serum solutions. (Author)