It has been reported, in animal models and recently in human beings, that intravenous fluorescein is taken up in peri lymph and may be useful as a tracer for the detection of perilymphatic fistulas. We attempted to reproduce the results of these animal experiments. Twenty-one middle ears of eight cats and four dogs were exposed. Fluorescein was given intravenously. Fluorescence was initially noted in transudates pooling in the oval and round window niches. Fistulas created with a straight pick produced a bright fluorescence in the leaking fluids, possibly from a ruptured small membrane vessel. Fistulas created with the carbon dioxide laser and with complete hemostasis demonstrated no fluorescence. We concluded that intravenously administered fluorescein causes dramatic fluorescence of vessels and transudates that may be interpreted falsely as fluorescence of perilymph. Fluorescence was not evident in perilymph when complete hemostasis was obtained