SUMMARYAn Australian isolate of tomato yellow top virus (TYTV‐A) was transmitted in the persistent manner by the aphidMyzus persicae.Its host range was mainly restricted to theSolanaceae, thoughCapsella bursa‐pastorisandGomphrena globosawere symptomlessly infected.TYTV‐A was purified fromPhysalis Joridana, using an enzyme‐assisted method in which the initial tissue homogenate was incubated with cellulase. Yields of purified virus were 100–900 μg/kg tissue and depended on the age of the infected plants. Maximum yields were obtained 4–5 wk after inoculation. The particles of TYTV‐A werec.24 nm in diameter, had a buoyant density of 1.34 in caesium sulphate and a coat protein mol. wt ofc.25.7 × 103.TYTV‐A was shown to be closely related serologically to potato leafroll virus (PLRV), TYTV from New Zealand and more distantly related to several other luteoviruses. An antiserum to TYTV‐A was used in enzyme‐linked immunosorbent assay tests to detect TYTV in field‐infected tomato plants and also luteoviruses from potato plants with leafroll symptoms. It is clear that TYTV‐A is a luteoviru