Human cytomegalovirus infection is a major cause of morbidity after lung transplantation. LIR-1 (leucocyte immunoglobulin-like receptor-1) is an inhibitory cell surface receptor that has high affinity for an MHC class I homologue (UL18) encoded by human cytomegalovirus. We aimed to investigate whether reactivation of human cytomegalovirus affects the expression of LIR-1. We measured LIR-1 expression on peripheral blood lymphocytes from 13 lung-transplant recipients and established human cytomegalovirus load using PCR. Eight patients developed cytomegalovirus disease. The percentage of cells expressing LIR-1 increased in the patients who developed cytomegalovirus disease several weeks before viral DNA was detectable by PCR. Measurement of LIR-1 expression might allow early identification of cytomegalovirus disease in lung-transplant patients.