Radial double-immunodiffusion, immuno-osmophoretic and enzyme-linked immunosorbent assay (ELISA) methods have been compared for the detection of Fiji disease virus (FDV) in infected sugarcane tissue extracts using an antiserum containing antibodies specific to FDV proteins and ds-RNA. ELISA was the most sensitive of these tests and detected only FDV-specific proteins byt not ds-RNA. Immuno-osmophoretic tests were less sensitive than ELISA but detected both the protein and ds-RNA antigens as distinct precipitin lines. Immunodiffusion tests were much less sensitive for the detection of FDV antigens than either ELISA or immuno-osmophoretic tests. FDV antigens were detected in leaves of virus-infected sugarcane, but only in tissues of the galls which develop in response to infection. Even ELISA failed to detect any antigens in normal tissues adjacent to galls. It is concluded that for the identification to FDV in infected surgarcane, it is necessary to observe galls which can then be tested for the presence of FDV antigens. Immuno-osmophoresis appears to be a satisfactory method for such tests.