Xanthotoxol (XT), 8-hydroxypsoralen, exhibited dose-graded sedative activity in dogs, cats, rats, mice and hamsters. At doses of 5-20 mg/kg intraperitoneally (i.p.) in cats and 3-100 mg/kg orally (p.o.) in dogs, XT blocked predatory mouse/rat killing behavior. In mice, XT (10-300 mg/kg i.p.)