The immune response of cattle and pigs to a vaccinia recombinant virus containing the fusion (F) protein gene of rinderpest virus was examined. Half the cattle and all the pigs gave humoral response to primary vaccination and all the cattle gave an anamnestic response to a second vaccination 28 days after the primary vaccination. All the cattle after a single or secondary vaccination were completely protected clinically after exposure to a lethal dose of the Saudi 1/81 strain of virus. Prior vaccination with another TK- vaccinia recombinant (VVCAT) suppressed, but did not abrogate, the immune response to the rinderpest F recombinant. The pigs gave a humoral immune response in the absence of any local reaction at the site of vaccination.