Disseminated infection with herpes simplex virus type 2 was identified in two patients 20 days after they had received kidney transplants from the same organ donor. Neither patient had neutralizing antibody to herpes simplex virus before transplantation, and both had herpes simplex virus isolated from surveillance cultures of urine before the onset of clinical symptoms. A clear focus of primary infection was not found in either patient. Analysis of the patients' isolates by DNA restriction endonuclease analysis strongly suggested that the strains were identical. These data implicate the allografts as the source of the viral infection.