Increasing experimental evidence suggests that gluten contains a toxic factor that may cause ultrastructural changes in the small intestine which mimic those found in patients with celiac disease. In addition, it has recently been proposed that the toxic factor of gluten is a protein very similar, if not identical, to a well known lectin, wheat germ agglutinin (WGA). Since the cytoskeleton forms the basis of the ultrastructural architecture of the enterocytes the present study was performed to investigate whether WGA has a direct effect on the cytoskeleton in Intestine 407 cells. Changes in the cellular content of filamentous actin (F-actin) in these cells were studied with the fluorescein isothiocyanate (FITC)-phallacidin assay. Cellular exposure to WGA led to a rapid reduction in the cellular content of F-actin (greater than 50%). Intracellular buffering of the cytosolic free calcium level using quin2 as a chelator of calcium totally abolished the WGA-induced reduction in F-actin content. However, increasing the cytosolic free calcium level by exposure to the calcium ionophore ionomycin did not affect the cellular content of F-actin. Ionomycin also failed to potentiate the effect of WGA on the cellular F-actin content. The present results show that WGA changes the organization of the cytoskeleton in Intestine 407 cells via a calcium-dependent mechanism, however, in addition to calcium, some other signal(s), possibly an increased turnover of the phosphatidylinositol cycle, is(are) also required.