Venular control of arteriolar perfusion has been the focus of several investigations in recent years. This study investigated (1) whether endogenous adenosine helps control venule-dependent arteriolar dilation and (2) whether venular leukocyte adherence limits this response via an oxidant-dependent mechanism in which nitric oxide (NO) levels are decreased. Using intravital microscopy, changes in arteriolar diameters and NO levels were assessed in the rat mesentery. The average resting diameter of arterioles (27.5 ± 1.0 µm) paired with venules with minimal leukocyte adherence (2.1 ± 0.3 per 100 µm length) was significantly larger than that of unpaired arterioles (24.5 ± 0.8 µm) and arterioles (23.3 ± 1.3 µm) paired with venules with higher leukocyte adherence (9.0 ± 0.5 per 100 µm length). The local superfusion of adenosine deaminase (ADA) induced significant decreases in diameter and perivascular NO concentration in arterioles closely paired to venules with minimal leukocyte adherence. However, ADA had little effect on arterioles closely paired to venules with high leukocyte adherence or on unpaired arterioles. To determine whether the attenuated response to ADA for the high adherence group was oxidant-dependent, the responses also were observed under tempol treatment (10^-4 M). In the high adherence group, tempol fully restored NO levels to those of the low adherence group; however, the ADA-induced constriction remained attenuated, suggesting a possible role for an oxidant-independent vasoconstrictor released from the inflamed venules. These findings suggest that adenosine- and venule-dependent dilation of paired arterioles may be mediated in part by NO, and inhibited by venular leukocyte adherence.