Thirty days after infection with the parasite Nippostrongylus brasiliensis, microcirculatory changes associated with worm allergen-induced anaphylactic shock in pentobarbital-anesthetized rats were studied. Allergen challenge decreased heart rate, mean arterial blood pressure, and cardiac output (CO) for 60 min, although CO increased markedly by 240 min. Blood flow (ml.min-1.g wet tissue-1) was reduced to most tissues, with the exception of the kidneys, hepatic arterial, heart, and brain, for 60 min. Depressed flow to the adrenals and enhanced flow to the kidneys, trachea, stomach, and mesentery were observed at 240 min. The percent distribution of cardiac output per gram wet tissue (%CO/g) increased initially to the kidneys, heart, liver, and cervical spinal cord, decreased to the spleen and cecum, and remained unchanged to other gastrointestinal tissues. The %CO/g to most tissues returned to normal by 60 min but decreased to the adrenals at 240 min. The intestine is an important organ affected by anaphylaxis in the rat, and the liver may participate in alleviating anaphylaxis.