Clinicians often do not consider the presence of more than one viral etiologic agent in respiratory infection, and in many cases they order diagnostics for influenza viruses or recently even only for A(H1N1)2009 virus. However, in a substantial number of patients with a respiratory tract disease, co-infection with various viral pathogens has been confirmed. Although the association between the occurrence of co-infection and substantially higher severity of disease is still unclear, a rapid and proper diagnostics of wide spectrum of viral respiratory pathogens reveals an accurate picture of the disease and is essential for appropriate therapeutic management and control of infection. In the present study we reported five cases of multiple respiratory infection in hospitalized immunosuppressed patients: two double infections with influenza virus (IV) type A/respiratory syncytial virus (RSV) type A and IV type A/coronavirus (CoV) OC43, one infection with four viruses - IV type A/RSV type A and B/CoV OC43, and two cases of mixed infections caused by five viral agents - IV type A and B/RSV type A and B/ parainfluenza type 3 or CoV OC43. Each patient had an underlying chronic disease and received immunosuppressive treatment. Despite a low number of tested specimens, our study shows that the inclusions of multiplex PCR methods for diagnostics of respiratory tract infections and the extension of diagnostic strategies by clinicians to detect viruses other than influenza are very important and make a contribution to identifying the true rate of co-infections and their correlation with the clinical symptoms and severity of disease.