Recurrent malignant pleural effusion occurs in approximately 50% of patients with metastatic tumors and their therapy is essentially palliative. The most used method is the chemical pleurodesis. However, we don’t know what would be the ideal time to submit the patient to the procedure, neither what the best sclerosing agent. The objective is to analyze if the progression of the pleural neoplastic disease is associated with the degree of fibrosis in mice subjected to pleurodesis with talc and nitrate, in animals injected with 10 thousand Lewis’s cells intrapleural. In this experimental study we used twenty C56-BL mice, with pleural cancer induced by injection of 10.000 Lewis cells/ml of 0.9% saline. On the third day of pleural disease, half of the animals were subjected to plerodese, 5 of them with talc at a concentration of 400mg/kg (called Group 3 Talc-“GT3”) and other 5 with silver nitrate in a concentration of 0.05% (called nitrate Group-“GN3”). On the seventh day of pleural disease, the remaining subjects were again divided into 2 groups of 5 animals (GT7andGN7) and subjected to plerodesis with the same substances and concentrations. All animals were sacrificed 7 days after pleurodesis, regardless of which group they belonged. All animals were pleural implants of cancer cells. Regarding the macroscopic findings were graded fibrosis in score been validated in other studies ranging from 0 (no fibrosis) to 4 (complete symphysis). In GT3 group, 2 animals had a score 2, and 2 animals obtained score 0.5. In the nitrate group (GN3) 3 animals had a score 0. In animals underwent pleurodesis after 7 days of illness, the talc group (GT7), 3 animals received a score of 0,2 and 2.5 respectively; the nitrate group (GN7) received scores of 0.5, 1 and 2. Microscopically, all had the presence of fibroblasts and fibrosis on visceral pleura. 2 blades each group (GT3 GN3, and GT7 GN7) were stained with picrosirius method for evaluating local fibrosis, and all had positive staining method including quantitation amount sufficient to further study. The animal control cutting blade, with only pleural disease had negative results. Animals with this number of implanted cells have sufficient survival and satisfactory answer to pleurodesis so we can quantify it according to the available methods. There was no weight loss or significant reduction in activity of the animals during time. Apparently, there is a greater amount of fibrosis in animals submitted to pleurodesis with talc.