During the period 1981-88 foot-and-mouth disease virus (FMDV) serotype O continued to be isolated from outbreaks in the Middle East. Field isolates submitted to the World Reference Laboratory have been examined in relation to reference strains by either complement fixation, virus neutralization or enzyme-linked immunosorbent assays. Most isolates were related to the European type O1 reference strains although strains emerging in late 1987 and 1988 were more closely related to O1/Manisa. In addition, FMDV isolates from Libya in 1981 and Syria in 1987 have shown very little relationship to these reference strains, although evidence of their persistence and spread has not been demonstrated.