Serological relationships among the 4 Australian strains of sugarcane mosaic virus, johnsongrass (JG), sugarcane (SC), Queensland blue coach grass (BC) and subgrass (Sabi), were compared using 2 variations of immune electron microscopy. Particles of each strain were counted after being trapped on grids coated with protein A and homologous and heterologous antisera (differential trapping) or were trapped with homologous antisera, coated with homologous and heterologous antisera (decoration), and photographed. Results obtained from the differential trapping and decoration methods both led to the conclusion that the JG strain is not related serologically to the other 3 strains, SC is closely related to BC and Sabi but is distinct from both. BC and Sabi are very closely related to each other. Results are discussed in light of previous reports that show that JG is related serologically to other strains of the virus.