Regional blood flow responses to 1-deamino-6-carba-(8-arginine)-vasopressin (dCAVP) were investigated in pregnant guinea pigs by the radioactive microsphere technique. Intravenous injection of 0.1 microgram/kg body weight caused a moderate rise in mean arterial blood pressure from 6.8 to 7.9 kPa, a significant reduction in tissue perfusion of the stomach, mammary gland, urinary bladder and vagina, and a significant increase in renal and cerebral blood flow. In a small number of animals given 1.0 microgram/kg of dCAVP, which evoked a strong pressor response, it was also possible to demonstrate a reduction in cutaneous and pancreatic blood flow and an augmentation of adrenal blood flow. Uterine and maternal placental blood flow did not alter significantly following administration of this vasopressin analogue.