Foot-and-mouth disease virus (FMDV) can spread by a variety of mechanisms, including, under certain circumstances, by the wind. Simulation models have been developed to predict the risk of airborne spread of FMDV and have played an important part in decision making during emergencies. The minimal infectious dose of FMDV for different species by inhalation is an important determinant of airborne spread. Whereas the doses for cattle and sheep have been quantified, those for pigs are not known. The objective of the study was to obtain that data in order to enhance the capability of simulation models. Under experimental conditions, forty pigs were exposed individually to naturally generated aerosols of FMDV, strain O1 Lausanne. The results indicated that doses under 100 TCID50 failed to infect pigs but doses of approximately 300 TCID50 caused short-term sub-clinical infection. The calculations suggested that a dose of more than 800 TCID50 is required to cause infection and typical disease.