The conditions required for the transport of foot-and-mouth disease (FMD) virus in the atmosphere over long distances and in sufficient concentrations to cause infection in exposed animals are described. Using these factors a series of 23 outbreaks of FMD in Europe, where the original outbreaks were separated from later outbreaks by sea passage, have been investigated. The findings obtained support the hypothesis that under certain conditions the airborne transmission of FMD over a long sea passage is possible.