From December 1991 to September 1992, 20 patients due to receive total body irradiation (TBI) prior to allogenic or autologus bone marrow transplantation were given granisetron (Kytril) in order to prevent intestinal (nausea and vomiting) early intolerance. TBI regimen was delivered on a fractional basis of six fractions, over 3 days. Twelve grays were delivered with a lung protection decreasing the pulmonary dose to 9 Gy. Granisetron (3 mg) was administered by a 5-min intravenous infusion, 1 h before TBI. Up to two further infusions were given if nausea or vomiting occurred. The pretreatment perfusion was sufficient to prevent nausea and vomiting in 10/20 patients, one additional post-treatment perfusion was necessary in 7/20 patients, and two in 1/20 patients. In 2/20 cases, nausea and vomiting persisted in spite of three perfusions. Excellent or good efficacy was noted in 15/20 patients and a minor (or no) efficacy in five. Granisetron appears to be superior to the conventional anti emetic schemes to prevent nausea and vomiting in patients receiving TBI for bone marrow transplantation.