Two live-attenuated parainfluenza virus type 3 (PIV3) candidate vaccines have completed Phase I trials in human infants and children. A bovine PIV3 that is antigenically related to the human PIV3 has been licensed to a biotechnology company that will pursue its further development. The second candidate, the cold-passaged (cp45) mutant of human PIV3, is being studied further under a CRADA between NIAID/LID and a pharmaceutical manufacturer. Infectious PIV3 has been recovered from cells transfected with PIV3 full-length cDNA in the presence of the needed accessory factors, and this new capability opens up the possibility for the rapid development of vaccines for PIV1, PIV2, and PIV3 using recombinant cDNA technology. A highly attenuated vaccinia virus vector (MVA), that should be completely safe for immunocompromised humans, was used to express the viral surface HN and F glycoproteins which are the major protective antigens of PIV3. Immunization of rhesus monkeys with the MVA-PIV3 recombinant viruses induced protection against replication of challenge virus in the lower, but not the upper, respiratory tract despite the mucosal administration of the recombinant vaccine candidate.