Intercellular adhesion molecule-1 (ICAM-1) plays an important role in inflammatory diseases. Cellular expression and shedding of ICAM-1 are up-regulated by cytokines, such as tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ). With an ELISA containing two monoclonal antibodies to human ICAM-1, we measured concentrations of circulating ICAM-1 in patients with tuberculosis. Prominently elevated values were found in miliary tuberculosis and in far advanced pulmonary tuberculosis but not in minimal or moderately advanced disease. The measurement of serum IFN-γ and TNF-α also revealed high concentrations of the cytokines in miliary tuberculosis and far advanced pulmonary tuberculosis. The circulating ICAM-1 values were significantly correlated to serum IFN-γ and TNF-α values. In the case of miliary tuberculosis and far advanced pulmonary tuberculosis treated with antituberculous drugs, the circulating ICAM-1 concentrations were gradually decreased to correspond with improvement of clinical symptoms and chest X-ray findings. The measurement of circulating ICAM-1 is useful to evaluate the severity of tuberculosis and to monitor disease activity during antituberculous drug treatment.