Filamentous viral particles were observed by electron microscopy in several banana plants without symptoms (Fig. 1). The same type of particles were also identified in mixed infections with the viruses responsible for diseases in banana: the cucumber mosaic virus (CMV) in banana plants developing unusual symptoms of necrosis, the banana bract mosaic virus (BBrMV) and the banana streak virus (BSV). Polyclonal and monoclonal antibodies were developed against particles purified from apparently healthy cv MBouroukou (Fig. 2) and cv Ducasse. These antibodies reacted with one protein of an estimated size of 30kD (Fig. 3). This serological reaction was obtained with banana samples infected by filamentous viral particles collected from banana germplasm collections at INIBAP and CIRAD-FLHOR Guadeloupe, from banana samples showing CMV symptoms and unusual necrosis and from BBTD infected banana samples. These viral particles, alone or in coinfection, were serologically related and maybe identical. Twenty-five percent of the germplasm studied was infected by the filamentous particle alone which seemed to be restricted to the AAB Musa genome. The comprehensive survey of the Musa collection at CIRAD-FLHOR in Guadeloupe revealed only vegetative dissemination. The particles involved in coinfection with CMV appeared to be related to severe attacks of the chlorosis disease and strongly correlated with necrosis symptoms (Fig. 4). It seemed to be propagated in the same way as CMV because the planting material was virus free. If these viral particles alone and in coinfection are the same particles, the opportunity to be in mixed infection would facilitate their propagation. In order to understand their role and to study their impact, an ELISA test combining polyclonal and monoclonal antibodies was developed.