Six compounds isolated from the EtOAc fraction of the dried roots of Angelica dahurica var. dahurica inhibited compound 48/80-induced histamine levels in mouse peritoneal cavity (in vivo). Bergapten, oxypeucedanin hydrate, and byakangelicin inhibited compound 48/80-induced histamine elevation at a dose of 25 mg/kg. Conversely, sec-O-acetylbyakangelicin [8-(2-acetoxy-3-hydroxy-3-methylbutoxy)-5-methoxypsoralenI enhanced compound 48/80-induced histamine elevation at a dose of 25 mg/kg, while phellopterin and oxypeucedanin had no effect.