Blood pressure, heart rate and plasma catecholamine levels were compared in non-pregnant and term-pregnant SP-SHR, SHR [ spontaneously hypertensive] and WKY female rats. Rats were anesthetized with halothane and the ventral caudal artery was cannulated. The pregnancy success rate for hypertensive females (SP-SHR and SHR) was significantly lower than for WKY females (P < 0.01). Pregnancy was associated with an increase in heart rate for females of each strain (P < 0.05). No differences were observed between pregnant and control females of the 3 strains with regard to blood pressure or levels of circulating catecholamines. Pregnancy is not attended by further increases in blood pressure or sympatho-adrenal activity in SP-SHR, SHR, or WKY females. Additional studies of SHR females may provide an experimental model for the evaluation and treatment of complications arising during pregnancy in patients with chronic hypertension.