Thirty-one selected patients with various haematological malignancies who received a 10 Gy-4 h total body irradiation (TBI) at the Institut Gustave Roussy 24 h before high dose cyclophosphamide for bone marrow transplantation, were prospectively evaluated for gastrointestinal symptoms, body temperature, consciousness, headache, xerostomia, parotiditis, ocular symptoms, blood pressure, and respiratory and cutaneous signs for 24 h. In spite of prophylactic administration of various anti-emetic agents, 90% of the patients experienced nausea and 80% experienced vomiting. An almost constant body temperature peak--up to 40.8 degrees C--was registered 6 h after the start of irradiation. No drowsiness was reported since the introduction of the new anti-emetic agent Ondansetron. Nearly half the patients (42%) complained of headache. The proportion of patients experiencing early (during TBI) xerostomia was 61%. 74% of patients complained of parotiditis in the first 24 h. Although this low dose rate whole body irradiation is not likely to be exactly replicated in many accidental human exposures, the incidence rate and the time-course of the observed prodromal phase symptoms may prove helpful for early triage in the case of accidental irradiation.