Daily slit-lamp biomicroscopic examination and daily virus cultures for six months of 20 herpes simplex infected rabbit corneas have been used to follow the natural course of this experimental infection. More than two months after the signs of primary infection had cleared completely, 13 of 20 eyes (65%) spontaneously released herpes simplex virus, yielding positive cultures for 1 to 11 days (average seven days). Most of these corneas showed spontaneous recurrence of clinical activity including dendritic figures. The high incidence of spontaneous reactivations stresses the need for critical assessment of studies reporting induced reactivation of experimental herpes simplex keratitis.