Floating sections from human brains immersed for more than forty years in formalin, or from brains freshly fixed for a short time are treated by KMnO4-Pal's modified solutions to suppress the endogenous peroxidase activity before using the peroxidase-antiperoxidase method (PAP), or to remove the autofluorescence of lipofuscin, which is very intense in brains from old patients, before using the immunofluorescence method. Following this, immersion of sections in NaOH and H2O2 allows for the demasking of antigenic sites. These treatments enhance the immunolabelling considerably, with results comparable to those obtained with freshly fixed tissues, and facilitate the discrimination between specifically and unspecifically stained structures.