SETTING: Parenchymal lung destruction accompanied by active tuberculosis is, at least in part, caused by host as well as bacillus metalloproteinases. Mycobacterium tuberculosis has been shown to stimulate MMP-9 expression in the lung of infected organisms.DESIGN: We have used quantitative zymography and computer-assisted image analysis to measure the levels of type IV collagenases in 20 serum samples of patients with active tuberculosis and in 23 serum samples of healthy volunteers.RESULTS: Mean levels of the serum MMP-9 were over three-fold higher in tuberculous samples compared with normal serum (P P CONCLUSIONS: We suppose that the elevation of serum MMP-9 levels in patients with tuberculosis is affected by the augmentation of synthesis and/or secretion of this enzyme by inflammatory cells in response to M. tuberculosis infection. The observed association between the serum MMP-9 level and the extent of radiological change suggests that the quantification of the serum level of this enzyme may constitute a supplementary test in pulmonary tuberculosis diagnostics.