The use of a panel of polyclonal antisera and monoclonal antibodies (MAbs) raised against West African isolates of rice yellow mottle virus (RYMV) in ELISA resulted in separation of 73 RYMV isolates into three distinct serogroups. Using a set of differential rice varieties, the serogroups could be correlated to two RYMV pathotypes. A relationship was found between serological properties of the RYMV isolates and their probable ecological origin. It was concluded that RYMV isolates originating in closely related agro-ecological zones displayed variability in coat protein and pathogenicity. This should be taken into account in developing tolerant or resistant rice varieties.