Newcastle disease virus (NDV) has antineoplastic and immunostimulatory properties, and it is currently being clinically tested in anticancer therapy. In order to analyze the immunostimulatory effects of NDV on bovine papillomatosis, we inoculated 14 cows subcutaneously with an attenuated vaccine containing the LaSota strain of NDV (LS-NDV). Four cows with papillomatosis served as controls. Serum samples were collected from each animal 1 h before and, 7 and 21 days after inoculation. In inoculated cows, on days 7 and 21 the mean antibody titers were log2 2.43 +/- 0.92 and log2 5.57 +/- 0.72 by haemagglutination inhibition (HI), and the mean levels of tumor necrosis factor-alpha (TNF-alpha) were 5.80 +/- 4.19 and 5.39 +/- 2.66 ng/ml by WEHI-164 cytotoxicity assay. Significant differences between inoculated and control animals were evident for antibody titers on day 21 and clinical scores on day 60. A correlation was evident between the TNF-alpha activities and clinical scores on day 21. The clinical observations at day 60 showed that the papillomas in five cows were completely resolved (36%), one animal had no alterations on clinical appearance of the tumor (7%), and papillomas in eight cows were regressed (57%). In conclusion, these results demonstrated that inoculation of LS-NDV vaccine stimulates an antibody response and limited increase in TNF-alpha activity and may enhance clinical recovery in bovine papillomatosis.