Cortinarius poisoning is generally caused by orellanine, a hydroxy bipyridine N, N-dioxide. This intoxication is characterized by acute nephritis which can lead to death without treatment. We reported a highly sensitive and simple fluorimetric technique to analyse orellanine by thin-layer chromatography on the basis of its characteristic photodecomposition into orelline. Using this procedure, we detected and assayed orellanine for the first time in plasma and renal biopsies of a woman who had deliberately ingested two fruit-bodies of Cortinarius orellanus. An early original treatment was carried out based on hemodialysis, combination plasmapheresis-hemoperfusion, and amino acids and diltiazem administration. These results indicate that it is now possible to make a precise diagnosis of orellanine poisoning.