DsRNAs were detected in 36 of 49 Monilinia fructicola isolates from stone fruit orchards in New Zealand. The dsRNA profiles were highly variable, even between isolates from a single tree. Comparison of pathogenicity on detached fruit, in vitro growth rate, and sporulation of 14 isolates showed no obvious correlation with presence of dsRNAs. Partially purified extracts from four isolates were examined for the presence of virus-like particles by transmission electron microscopy. One isolate contained 45 nm isometric particles similar in appearance to totiviruses and partitiviruses. A second isolate contained 200-250 x 25 nm rigid rods similar in appearance to the plant pathogenic tobraviruses and furoviruses. This is the first report of the presence of viral-like agents in the brown rot fungus Monilinia fructicola.