Diagnosis of echovirus 30 meningitis was established by recovery of the virus from the cerebrospinal fluid (CSF) of four patients during a small outbreak. In three patients, viral isolation was easily achieved with human diploid tissue cultures (WI-38) whereas the same fluids failed to induce a cytopathic effect in monkey kidney tissue cultures. In one instance, isolation of the virus from CSF was successful in monkey kidney tissue but cultures could not be transmitted serially in these cells. There was no pleocytosis of the CSF in one patient, minimal pleocytosis in another, and more than 500 polymorphonuclear leukocytes per millimeter in another. The results show the value of human diploid cells for diagnosis in this type of infection and indicate variations that can occur in the cellular content of the CSF.