Rifampin increased nitric oxide production and inducible nitric oxide synthase expression in alveolar cells stimulated with cytokines. Nitric oxide concentrations after induction with cytokines, cytokines with 10 microg/ml rifampin, and cytokines with 50 microg/ml rifampin were 3.2, 4.5, and 8.8 microM, respectively (P < 0.02 versus cytokines alone). This indicates that rifampin modulates the immune response.