In order to determine the pathogenesis of gastric mucosal lesions induced by whole-body vibration (WBV), the effects of WBV (3.0 G, 10 Hz, 90 min) on gastric mucosal blood flow (GMBF), plasma corticosterone (COR) and catecholamines (CA), and gastric ulcer formation were investigated in relation to the effects of forced water-immersion stress (FWI) upon the same parameters. While WBV increased GMBF during the exposure, FWI decreased it both during and after the stress. No difference in the severity of ulcer formation between the WBV and the FWI groups was seen. Both WBV and FWI increased plasma COR and CA, although the degree of the increase in COR that accompanied WBV was less than that associated with FWI. Truncal vagotomy attenuated the reduction of GMBF and the extent of ulcer formation that occurred with FWI, but promoted a reduction of GMBF with WBV. These findings indicate that ulceration induced by WBV may be caused primarily by its direct and specific mechanical actions and not by indirect, central nervous system effects known to be important in the pathogenesis of ulcerations produced by mental stress.