Experimental stroke is associated with increased levels of brain Ang II [30,31]. In the present study, Ang II levels also increased in both male and female human cerebral arteries after 48 h organ culture. Ang II immunoreactivity was localized to both VSMCs and endothelial cells. Although there were no sex differences in Ang II expression, our potency **data** from the culture model suggest that cerebral arteries in men would be more sensitive to any stroke-related rise in Ang II. in the same tissue. Each point represents mean 6 SEM; females, n = 6 and males n = 8 to 9. The concentration-response curves for each agonist were analyzed with extra sum-of-squares F test to determine if the curves were statistically different between male and female arteries (P-values are presented above the curves). Exact values and statistical significance for individual parameters such as E MAX and pEC 50 are found in Table 1 The present study also showed sex differences in the contractile responses of human cerebral arteries to ET-1. After organ culture, a biphasic concentration-response curve to ET-1 was seen in male arteries, consistent with activation of both ET A and ET B receptors. However in female human cerebral arteries, ET-1 produced only a monophasic concentration-response curve reflective of ET A receptor-mediated contraction. Thus male and female arteries had similar ET A -mediated responses, but female arteries showed little or no response via the high affinity ET B receptor. It should be noted that three of the male patient samples demonstrated no or weak ET B receptor-specific vasoconstriction. Although the reason for these observations cannot be explained, medication history and age of these patient samples were not any different from the patient samples showing strong ET B receptor-mediated vasoconstriction.