Studies of endothelial regulation of microvascular function have been hampered by the technical difficulty of removing the endothelium without damaging the vascular smooth muscle cells. This study presents a novel method of endothelial damage and lysis based on the facts that endothelial cells express specific antigens and that complement reacts with antibody/antigen complexes, causing cell lysis. We isolated and perfused rabbit glomerular afferent arterioles in vitro and examined vascular responses before and after treating them with an antibody against factor VIII-related antigen and complement. The treatment consisted of perfusing afferent arterioles with medium containing the antibody and complement for 10 minutes, followed by a 20-minute washout period. Before treatment, acetylcholine and the calcium ionophore A23187 (receptor- and nonreceptor-mediated endothelium-dependent vasodilators, respectively) dilated norepinephrine-preconstricted afferent arterioles, whereas neither dilated the arterioles after treatment, suggesting loss of endothelium-dependent vasodilation. In contrast, responses to nicardipine and norepinephrine (endothelium-independent vasodilator and constrictor, respectively) were not altered by the treatment, indicating intact vascular smooth muscle cell function. Transmission electron microscopy revealed that the antibody- and complement-treated arterioles had various degrees of endothelial damage, including areas of detachment from the basement membrane and marked loss of the number and structure of mitochondria, but no evidence of vascular smooth muscle cell damage. These results indicate that treatment with anti-factor VIII-related antigen antibody and complement is an effective method for eliminating endothelium-dependent vasodilation without altering endothelium-independent responses. Thus, this method may be useful for studying the functional role of the endothelium in microvessels.