Intercellular adhesion molecule-1 (ICAM-1) induction on hepatocytes was investigated in relation to acute liver allograft rejection, CMV infection, and systemic bacterial infections. Twenty-four liver transplant recipients underwent an episode of acute rejection, 13 developed a symptomatic clinical CMV infection, and 7 had bacterial sepsis. Seven recipients without rejection or infection complications were used as controls. All rejection episodes monitored by frequent FNABs were reversible, and lymphocyte and lymphoid blast-dominated with a with peak of inflammation (7.2±3.9 corrected increment units [CIU]). The rejections were treated with high-dose steroids, and the inflammation subsided within one week. ICAM-1 was demonstrated from fine needle aspiration biopsy (FNAB) preparations by a monoclonal antibody and immunoperoxidase staining. ICAM-1 was not detected on the hepatocytes immediately after transplantation or in control patients, but was always seen during rejection. ICAM-1 appeared 1–5 days before the onset of inflammation in FNAB. The intensity of ICAM-1 expression increased toward the peak of inflammation and subsided together with inflammation. During CMV infection a mild immune activation was seen in FNAB (peak 2.5±0.8 CIU) and in blood. An intense ICAM-1 induction also preceded the immune activation caused by CMV, and subsided slowly with successful antiviral treatment. In addition, a slight ICAM-1 induction on the hepatocytes was recorded during bacterial sepsis. ICAM-1 induction on hepatocytes appears to be linked with an early phase of immune response, and it even precedes the lymphoid activation of rejection. However, several infections, such as CMV and bacterial infections, raise an immune response and may also induce ICAM-1. In conclusion, ICAM-1 induction on hepatocytes can be considered an early, though unspecific, marker for acute liver allograft rejection.