An experimental in vitro model has been developed in order to determine whether Blastocystis hominis is able to trigger inflammatory cytokine response in colonic epithelial cells. After 24 h incubation of B. hominis with the cell lines HT-29 and T-84, B. hominis cells were not able to cause cytopathic effects, but significant increases in the release of the cytokines IL-8 and GM-CSF could be observed. However, after the first 6 h of co-incubation, the production of IL-8 was not increased in HT-29 cells, and even reduced when Escherichia coli (bacteria or lipopolysaccharide) was present during co-incubation. Similar effects were observed using supernatants of B. hominis culture. These data indicate that B. hominis induces as well as modulates the immune response in intestinal epithelial cells, and we conclude that different pathophysiological events may occur during B. hominis infection.