The effect of various treatments on the Sudanophilia of the mineralizing fronts of hard tissues has been examined. We have shown that a variety of organic solvents. but not all lipid unmasking protocols. expose Sudanophilic lipids at the mineralizing fronts of dentine, enamel matrix, bone and cartilage by the extraction of a substance which is not Sudanophilic. A variety of organic solvents, but not all extraction protocols. abolish Sudanophilia at the mineralizing fronts of bone and cartilage. The present study indicates that only solvent mixtures containing methanol abolished Sudanophilia at the mineralizing fronts of dentine and enamel matrix.