Recent research has revealed a few cases in which fungal viruses exert strong effects on their fungal hosts (positive or negative), or on other symbionts of the infected fungi.  Most fungal virus studies focus on viruses of economically important fungi such as human or plant pathogens.  Nothing is known about the prevalence and diversity of fungal viruses in nature.  In this study, we surveyed virus diversity in a community of fungi associated with the parasitic plant dodder (Cuscuta pentagona) and its most frequently infected host plant, western ragweed (Ambrosia psilostachya), at three sites on the Tall Grass Prairie Preserve in Pawhuska, OK.  At least 11 genera of fungi were isolated from surface-sterilized tissues of dodder and parasitized ragweed.  These fungi, including Alternaria, Stemphylium, Cladosporium, Phoma, and Cercospora, may be latent saprotrophs, latent pathogens, or endophytes.  After dsRNA extraction of 132 representative fungal isolates, followed by agarose gel electrophoresis, we found band patterns consistent with viruses in approximately 15% of samples.  We conducted RT-PCR on these samples, using random hexamers, and obtained partial sequences of viruses representing the Totiviridae, Hypoviridae, Endornaviridae, and Astroviridae (determined from BLASTX searches in GenBank).  So far, we have not recovered more than one representative of a particular virus among multiple fungal isolates, indicating that diversity of fungal viruses may be very high.  Thus, fungal viruses may represent a frontier of cryptic biological diversity with the potential to strongly influence the fitness and ecology of their fungal hosts and associated plants.