The air of loose-boxes holding pigs affected with swine vesicular disease was sampled for virus. In the multistage impinger virus to a titre of 10(2.6) TCID 50 was associated with particles greater than 6 mum., 10(1.6) with particles 3-6 mum. and 10(1.4) or less with particles less than 3 mum. In the noses of workers in contact with the pigs for periods not less than 5 min., virus to a titre of 10(2.4) TCID 50 was found. Virus was recovered from the air for 2-3 days during the disease and maximum titre in pigs infected by injection or by contact occurred on the second to third day after generalization of the lesions. The amounts of virus were about 160-fold less than those recovered from pigs affected with foot-and-mouth disease, and the quantity and time of excretion suggest that the source of swine vesicular disease virus in the aerosol may be from the lesions and skin rather than from the respiratory tract.