The contribution of cell culture systems in the diagnosis of viral infections has been well recognized over the years. Not only did such systems make possible the direct isolation and identification of viruses, but also the production of viral diagnostic reagents for rapid diagnosis, the evaluation of antiviral agents, and the production of vaccines for the control of viral diseases. Although many reagents for rapid detection of viral antigens/genomes are currently available, none will make possible discoveries of new viral agents. Thus sensitive cell culture systems are still essential for the rapid and accurate diagnosis of viral infections. Since, as yet, no single cell culture system is susceptible to all viruses, the constant search for additional sensitive cell culture systems for detecting those unknown and/or currently non-cultivable viral agents continues to be an open area of investigation in the field of diagnostic virology.