Introduction. Cucumber mosaic virus (CMV), genus Cucumovirus, is distributed worldwide; it is a common pathogen of Musa spp. and it is present in all banana-producing areas. Materials and methods. Banana and plantain (Musa) leaf tissues were collected from six major Musa-growing states of Southern Nigeria in August 2000. A broad-spectrum CMV polyclonal antibody was used in Protein A Sandwich (PAS) ELISA to detect CMV isolates, while a CMV subgroup I-specific polyclonal antibody was used in DAS-ELISA to separate subgroup I isolates. Results. Of 108 Musa leaf samples collected, 76 samples (70.4%) reacted positively with the CMV polyclonal antibodies used, in which 32 samples (42.1%) belonged to CMV subgroup I. Edo and Ondo states had low CMV subgroup I incidence of 13.6% and 17.2%, even though both states had high CMV incidence of 63.6% and 62.1% in infected samples, respectively. Imo state had the highest CMV incidence of 72.4% and subgroup I incidence of 55.2%. Of the 32 leaf samples infected with CMV subgroup I, 18 samples expressed one type of viral symptom such as interveinal chlorosis, chlorotic streaks, leaf puckering and crisp deformed leaf. Thirteen other samples expressed two or three viral symptoms, showing either vein thickening or general leaf chlorosis and any of the former symptoms. One asymptomatic leaf tissue was also infected with the virus. Discussion. Our results confirm that subgroup I and other subgroups are responsible for CMV infection in Musa species in Nigeria. The detection of CMV over a large geographical area underscores the importance of virus control measures. CMV can be controlled by use of virus-free suckers.