Trypanosoma cruzi infection is known to confer resistance to tumor development in mice, and in-vitro studies have shown the toxic effects of parasite extracts on cancer cell cultures. Investigations in which T. cruzi molecules exhibit antitumor activity have just begun. Here, we used a tumorigenic cell line Tm5, derived from mouse melanocytes melan-a, to test the effect of J18, a recombinant protein based on T. cruzi surface molecule gp82 fused to glutathione-S-transferase (GST). J18 induced actin cytoskeleton disruption in Tm5 but not in melan-a cells. Several changes indicative of apoptosis were detected in Tm5 melanoma cells but not in melan-a cells treated with J18, such as the flipping of phosphatidylserine from the inner to the external side of the plasma membrane, altered nuclear morphology, DNA fragmentation, increase in mitochondria depolarization, and in caspase-3 activity. Retention of NF-kappaB in the cytoplasm was another alteration observed specifically in J18-treated Tm5 cells. No such alterations were found in Tm5 cells treated with GST. In-vivo experiments showed that C57BL/6 mice inoculated with Tm5 cells, treated at the site of tumor cell inoculation with J18, developed tumors of smaller size than mice treated with phosphate-buffered saline or GST and survived longer.