Sponge-induced angiogenesis in mice and pharmacological reactivity of the neovasculature have been determined by a fluorimetric method. Pharmacokinetic studies following subcutaneous, intradermal, and intraimplant administration of sodium fluorescein resulted in a biphasic curve from which estimation of t1/2 for absorption and elimination of the dye were possible. Following topical injection of the dye at days 1, 4, 7, 10, and 14 postimplantation, measurement of fluorchrome generated emission in the systemic circulation reflected the development of blood flow in and around the implants and the interaction of the angiogenic site with the systemic circulation. The t1/2 values for the fluorescence peak in the bloodstream decreased steadily from an initial value of 6.41 +/- 0.28 min (avascular implant) to 2.78 +/- 0.23 min in fully vascularized implants (day 14). The reactivity of the neovasculature to ET-1 was dose-dependent and similar to the skin vasculature. By contrast, no reactivity to histamine was detected in the implant blood vessels, whereas it was present in the skin. These results show that the pharmacological response of the neovasculature differs from the response of mature blood vessels. The angiogenic stimulus (bFGF, 300 ng daily) decreased t1/2 for the fluorescence peak, whereas dexamethasone (1 mg/kg) increased it. Parallel histological studies corroborated the functional findings. These observations indicate the suitability of this assay to study angiogenesis, functional and pharmacological characterization of the neovasculature, and the interaction of the angiogenic site with the systemic circulation.