In a study of varicella-zoster virus, one strain isolated from a patient with varicella and one strain from a patient with zoster were grown in a range of different cell cultures. The viruses grew in human amnion, human thyroid, human embryo lung, HeLa, rhesus monkey kidney, vervet monkey kidney and V3A cultures. They behaved identically, giving similar cytopathic changes in the same range of cell cultures. Neither virus could be readily obtained in a cell-free state. The isolation of varicella-zoster viruses in cell cultures was accomplished from vesicle fluids of 15 patients with chickenpox and one patient with zoster, and from lung tissue of a fatal case of chickenpox and a fatal case of zoster. Virus was not isolated from the urine of 23 patients with chickenpox and one patient with zoster, nor from the ganglia of the fifth cranial nerve of 66 elderly persons who had died from causes other than chickenpox and zoster. Both viruses in cell cultures were stored satisfactorily for several years at either -65° or -184°C and human thyroid cultures were the most suitable cultures for their subsequent recovery.