Tumor necrosis factor (TNF) causes regression of advanced cancers when used in isolation perfusion with melphalan; evidence suggests these effects are mediated via selective yet uncharacterized actions on tumor neovasculature. A novel derivative, colloidal gold bound TNF (cAu-TNF) has been shown to have similar antitumor effects as native TNF with less systemic toxicity in mice. These studies were done to determine their effects on tumor neovasculature, using in vivo video microscopy. Female C57BL/6 mice bearing 20 mm(2) MC38 or LLC tumors that are TNF sensitive and resistant tumors, respectively, had dorsal skinfold chambers implanted. The rate of interstitial accumulation of Texas red fluorescently labeled albumin in tumor and normal vasculature was measured after intravenous TNF, cAu-TNF or PBS. Changes in interstitial fluorescent intensity over time were quantified as a reflection of alterations in vascular permeability. MC38 bearing mice treated with TNF or cAu-TNF demonstrated a rapid, selective and significant increase in tracer accumulation in areas of neovasculature compared to those of normal vasculature. Experiments in LLC tumor bearing mice showed similar results. Monoclonal antibody against tissue factor partially abrogated the effects of TNF on MC38 neovasculature. These data provide direct evidence that TNF and cAu-TNF selectively and rapidly alter permeability in tumor neovasculature; a phenomenon that may be exploited to enhance selective delivery of chemotherapeutics to tumor.