Two double-stranded ribonucleic acid (dsRNA) elements were detected in an isolate of the clavicipitaceous grass endophyte Epichloë festucae obtained from an asymptomatic Festuca rubra plant. No dsRNA was detected in three other isolates of E. festucae. The size of the two dsRNA elements isolated from mycelium was of 5·2 and 3·2 kbp. Hybridization experiments with a cDNA probe complementary to the 5·2 kbp dsRNA showed that there was no sequence similarity between the dsRNA elements. Isometric virus-like particles of about 50 nm in diameter were observed by electron microscopy in sucrose-gradient purified virus preparations from the isolate containing dsRNA. The 5·2 kbp dsRNA element was present in the partially purified virus preparations, suggesting that this element is encapsidated. There was no difference with respect to growth rate or colony morphology between the dsRNA containing and dsRNA-free isolates. The presence of dsRNA and virus-like particles suggests the presence of a mycovirus in the Vit5 strain of E. festucae.