ABSTRACTFluorescent cyclic decapeptides, the so-called cortinarins, have been claimed to cause, or at least contribute to, the nephrotoxicity of the mushroomCortinarius speciosissima.As the structural elucidation of the cortinarins described in the literature is doubtful, the proposed structures must be disputed. In addition, the present study demonstrates that, on analysis of the fluorescent zones exhibiting the chromatographic behavior described for the cortinarins, only steroids are detectable. Our analytical results indicate that the fluorescence characteristic forCortinarius speciosissimaextracts is mainly due to ergosta-4,6,8(14),22-tetraen-3-one. Furthermore, we did not find any substances referable to cortinarins in extracts of mushrooms originating from different locations or collected in different years. Orelline, a photoproduct of the nephrotoxin orellanine contributes to the fluorescence but shows completely different chromatographic behavior.