Interleukin-6 is a multifunctional cytokine that has been shown to be increased in some pathological conditions involving the respiratory system such as those experimentally induced in animals or spontaneously occurring in humans. Experimental data demonstrating that interleukin-6 plays a significant role in commonly occurring respiratory system inflammatory diseases are reviewed here. Those diseases, i.e. asthma and chronic obstructive pulmonary disease, are characterised by mechanical derangements of the respiratory system, for the most part due to increased elastance and airway resistance. Recent findings showing that interleukin-6 has a causative role in determining an increase in airway resistance are reviewed. The end-inflation occlusion method was used to study the mechanical properties of the respiratory system before and after interleukin-6 administration. The cytokine was shown to induce significant, dose-dependent increments in both the resistive pressure dissipation due to frictional forces opposing the airflow in the airway (ohmic resistance) and the additional resistive pressure dissipation due to the visco-elastic properties of the system, i.e. stress relaxation (visco-elastic resistance). There were no alterations in respiratory system elastance. Even when administered to healthy mammals, interleukin-6 determines a significant effect on respiratory system resistance causing an increase in the mechanical work of breathing during inspiration. IL-6 hypothetically plays an active role in the pathogenesis of respiratory system diseases and the mechanisms that may be involved are discussed here.