Using the intrabronchial orthotopic propagation method, we evaluated the biological characteristics of human adenocarcinoma cell lines in vivo and examined the expressions of matrix metalloproteinase-2 (MMP-2) and -9 (MMP-9) and their related proteins. Nine human lung adenocarcinoma cell lines, including A549, NCI-H23, NCI-H322, NCI-H358, Calu-3, PC-14, LC-2/ad, RERF-LC-KJ and PL16T, were injected into the peripheral bronchi of mice using this method. The mice were sacrificed at 4 and 8 weeks after tumor cell propagation and the lungs and other organs were observed macroscopically and histologically. We classified the adenocarcinoma cell lines, according to their intrapulmonary tumorigenicity, into the following three groups: (A) those that showed a high incidence of intrapulmonary implantation (>50%) (A549 and NCI-H358). A549 showed mediastinal lymph node metastasis and pleural dissemination; (B) those that showed a low incidence of intrapulmonary implantation (PC-14, NCI-H322, NCI-H23, Calu-3, and LC-2/ad); (C) those that showed no tumorigenicity in the lung (RERF-LC-KJ and PL16T). In order to characterize the biological differences between each cell line, we investigated the expressions of MMP-2 and MMP-9 and their related molecules by northern blot analysis. The expressions of MMP-2 and MMP-9 and their activators (membrane-type 1-MMP and urokinase-type plasminogen activator) were thought to be associated with the growth, invasion and metastasis of the human lung adenocarcinoma cell lines examined.