Plasminogen activation is believed to be critical to the progression of oral squamous cell carcinoma by facilitating matrix degradation during invasion and metastasis, and high levels of urokinase plasminogen activator (uPA) and plasminogen activator (PA) inhibitor-1 (PAI-1) in tumors predict poor disease outcome. We describe the development of a novel method for studying PA in oral cancer that combines the sensitivity and specificity of zymography with the spatial resolution of immunohistochemistry. Laser capture microdissection (LCM) was combined with plasminogen-casein zymography to analyze uPA, tissue PA (tPA), uPA-PAI-1 complexes, and tPA-PAI-1 complexes in 11 tumors and adjacent non-malignant epithelium from squamous cell carcinomas of the tongue, floor of mouth, larynx, and vocal cord. uPA was detectable in all tumor samples analyzed, uPA-PAI-1 complexes in three samples, and tPA in nine. PA was detectable in as little as 0.5 microg protein lysate from microdissected tumors. In all specimens, uPA expression was highly increased in tumor tissue compared to adjacent non-malignant tissue. In conclusion, LCM combined with zymography may be excellently suited for analyzing the prognostic significance and causal involvement of the plasminogen activation system in oral cancer.