Removal of the hMPV M2-2 gene resulted in up-regulation of viral transcription, although there was no alteration in the level of genomic RNA. This had been observed previously for the respiratory syncytial virus (RSV) M2-2 gene as well as for hMPV [14] . Deletion of RSV M2-2 resulted in higher levels of viral transcripts compared to wt RSV. Based on these observations it was postulated that the RSV M2-2 is involved in regulating the balance between transcription and genome replication [24, 25] . Our observation that the levels of rhMPV transcripts peaked at day 3 p.i., while the levels of rhMPV/ΔM2-2 transcripts remained high through day 4 p.i. is also consistent with a higher level of viral transcripts in rhMPV/ ΔM2-2 infected cells. Thus, deletion of the hMPV M2-2, like its RSV counterpart, appears to cause aberrant regulation of viral transcription.