Syrian Golden hamsters are highly permissive for hMPV replication and were used to assess the attenuation of rhMPV/ΔM2-2 [14, 18] . Groups of 8 hamsters were inocu-lated on day 0 with 10 6 PFU of wthMPV/NL/1/00, rhMPV or rhMPV/ΔM2-2. Both the recombinant viruses were P3 stocks. On day 4, titers of virus in the nasal turbinates and lungs were compared. As expected, the titers of wthMPV/ NL/1/00 and rhMPV in nasal turbinates and lungs were comparable (Table 2) . However, the titers of rhMPV/ΔM2-2 were 3.7 log 10 PFU/gm lower in the URT and 1.8 log 10 PFU/gm lower in the LRT, relative to rhMPV titers. Therefore, rhMPV/ΔM2-2 was approximately 10,000-fold and 100-fold more restricted in the URT and LRT, respectively, compared to rhMPV.