1. To examine possible changes in vascular reactivity to exogenous bradykinin (BK) and the possible role of endogenous BK in reduced mesenteric vascular reactivity in pregnant rats. The authors studied the effects of Hoe 140 on systemic depressor responses to BK and on mesenteric vascular reactivity in in situ blood-perfused mesenteric resistance vessels of 18-20 day pregnant and age-matched non-pregnant Wistar-Kyoto rats (WKY). 2. Mean intra-arterial blood pressure (MBP) of pregnant rats was lower than non-pregnant controls. Basal mesenteric perfusion pressure (BPP) was slightly, but not significantly, reduced in the pregnant group. Neither MBP nor BPP was significantly influenced by Hoe 140 (1 mg/kg. s.c.) 3. Systemic depressor responses to BK (1-30 micrograms/kg, i.v.) were significantly increased in pregnant rats at 1 and 3 micrograms/kg. Hoe 140 completely abolished systemic depressor responses to BK in either pregnant or non-pregnant animals. 4. Mesenteric vascular responses to regional administration of noradrenaline, electrical stimulation of sympathetic nerve and angiotensin II were overall decreased in pregnant compared with non-pregnant groups, but those responses were not significantly affected by Hoe 140 in either groups. 5. The results suggested that although systemic depressor responses to exogenous BK were increased, endogenous BK does not contribute to decreased mesenteric vascular reactivity in vivo in pregnant WKY.