The use of the epidermal-like cell line CaCo2 and the efficient propagation of viruses from clinical material for diagnostic purposes are reported. Virus replication was observed by cytopathic effects and/or immunofluorescence. The following viruses replicate in CaCo2 cells: enteroviruses (coxsackie B1-B6, poliovirus types 1-3, most echoviruses and coxsackie A viruses), adenoviruses, herpes simplex types 1 and 2, measles, respiratory syncytial, parainfluenza type 2 viruses, and to a lesser extent rubella and mumps viruses. CaCo2 cells were used in neutralization tests for the diagnosis of enteroviral infections.