A persistent latent infection of human embryo fibroblasts by reovirus type 3 was found to be due to the continuous infection of a small proportion of the cells. Super‐infection of these cultures by herpes simplex virus resulted in the destruction of the monolayers by the herpes virus without any obvious signs of interference. Electron microscopic examination of these doubly infected cultures showed the presence of multi‐nuclear blebs and an unusual, “condensed‐mass”, form of intranuclear herpes virus. The implications of these findings are discussed. Copyright © 1968 Wiley‐Liss, Inc., A Wiley Company