Our objective was to investigate the role of matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) and their cellular sources in childhood asthma. We used 12 controls and 16 asthmatic children. The levels of MMP-9 and TIMP-1 in bronchoalveolar lavage (BAL) cells of asthmatic children were measured immunocytochemically. The positive level index, defined as the percentage of positive-stained cells x average optical density, was used to assess the expressing levels of MMP-9 and TIMP-1. The percentages of eosinophils and mast cells in bronchoalveolar lavage fluid (BALF) of asthmatic children were increased. Levels of MMP-9 and TIMP-1 in BAL cell of asthmatic children were increased significantly at about 30- and 35-fold relative to the controls, respectively. These results suggest that both MMP-9 and TIMP-1 contribute to tissue remodeling. MMP-9, which mediates the degradation of extracellular matrix (ECM), is increased significantly in the early or acute stage and may play a role in ECM degeneration. Excessive TIMP-1 may be synthesized following MMP-9 production when the body tries to repair the damage, which results in excessive deposition of ECM component.