Levels of the pro-inflammatory cytokines TNF-x and TNF-y were measured from the time of infection to the time of complete clearance of non-typeable Haemophilus influenzae (NTHi) from the lung in immune and non-immune rats. Mucosal immunization facilitated production of significant levels of TNF-x as early as 30 min post-pulmonary challenge with NTHi in immune animals. Following the peak at 2h, rapid decline of TNF-x levels occurred from the alveolar spaces. Levels of TNF-x in non-immunized animals increased at a slower rate, peaked at a lower concentration and were slower to decline. The significantly larger number of macrophages seen in the immune animals at 1 h after bacterial challenge could partially account for the higher levels of TNF-x. interferon-y was not detected in immune or non-immune rats at any time point before NTHi clearance after pulmonary challenge. Study of the kinetics of TNF-x release demonstrates that immunized animals control the release of pro-inflammatory cytokines more effectively than non-immunized animals for enhanced clearance of bacterial infection from the lungs