Human metapneumovirus (hMPV) and human respiratory syncytial (RSV) virus cause mild to severe infections of the respiratory tract in all age groups. So far, several cell lines derived from respiratory tissues have been identified to support replication of both viruses. Unfortunately, titers attained during replication differ between the both viruses within one cell line despite equal infection conditions, on the one hand giving raise to the assumption that the individual susceptibility may vary in dependence of the virus, and, on the other hand, making it difficult to compare results between both viruses. Low titers may cause problems in experiments such as animal trials, in which high titers in low volumes are a prerequisite for successful experiments. The advantages are described of the use of a human cell line (normally used for hepatitis viruses research) susceptible for RSV and hMPV in which both viruses replicate to comparable and high titers. It is also shown that the cell line can also be used for applications such as cell viability tests. Cell viability tests can be used as reciprocal determination tests of viral titers and therefore offer the opportunity to replace classical virological tests such as TCID(50). The cell line can be also used for high throughput applications like drug screening, making it a useful tool for screening for antiviral compound active against RSV and hMPV.