Polymerase chain reaction (PCR) assays were used to amplify herpes simplex virus type 1 (HSV-1) thymidine kinase (TK) sequences in DNA extracted from formalin-fixed, paraffin embedded corneas of patients undergoing corneal transplantation. PCR reamplification with an internal (nested) set of primers was required for detection in 10 of the 12 positive corneas indicating very low abundance of viral sequences. Three of the positive corneal samples were from failed corneal grafts. Overall, TK sequences were detected in 8 of 11 corneas from subjects with a past history of herpes keratitis and in 4 of 11 corneas from subjects with no past history of herpetic eye disease.