Field surveys were undertaken in 1997–1999 across five ecological zones in Nigeria to collect isolates of Maize streak virus (MSV), genus Mastrevirus. Apart from maize (Zea mays L.), 15 other grass species were found with MSV symptoms in Nigeria. These hosts showed two types of symptoms viz: mild (with or without mottle) or severe (typical symptoms in maize). When Cicadulina storeyi China was used to attempt transmission of these isolates of MSV to seedlings a susceptible maize hybrid CML 254 X CML 247, six isolates were not transmissible to maize. Seven isolates that were transmissible to maize produced mild symptoms. The viral agents causing typical or severe streak symptoms in Axonopus compressus (Sw.) P. Beauv., Brachiaria distichophylla (Trn.) Stapf, Dactyloctenium aegyptium (Linn.) P. Beauv. and Setaria barbata (Lam.) Kunth produced symptoms that were typical of MSV in farmers fields, when transmitted to maize. Out of 33 plant species that seedlings were challenged with MSV, only eight proved susceptible. Four of them showed mild symptoms while the other four showed severe symptoms of MSV. Only three isolates collected during the surveys did not react with a MSV polyclonal antiserum produced in mice in Double Antibody Sandwich-Enzyme-Linked Immunosorbent Assay (DAS-ELISA). These isolates were found in Andropogon gayanus Kunth (from Kaduna), Thelepogon elegans Roth ex Toem & Schult (from Kadawa) and Rottboellia cochinchinensis (Lour.) Clayton (from Jos) exhibited mild streak/mottle symptoms. Specific monoclonal antibodies, raised against MSV, reacted with 12 out of 25 samples tested. The DAS-ELISA data also showed significant variation in concentration of the virus in the different plant hosts. The relationship dendogram through SDS-PAGE among eight purified virus isolates show 55–90% variation. At 0.55 coefficient of similarity, the dendogram divided the samples into two groups while at 0.9 coefficient of similarity, the 8 isolates were identified as distinct genetic entities.