The present invention relates to a method for detecting and/or measuring the concentration of fluoride (F.sup.-) or hydrogen fluoride (HF) in a sample, comprising the steps consisting of bringing said sample, in aqueous solution, into contact with a silylated organic compound in order to obtain a measurement solution, with said silylated organic compound being desilylated when it is in the presence of hydrofluoric acid or a fluoride, with the silylated organic compound and the desilylated organic compound being able to be detected and/or measured separately from each other; and detecting and/or measuring, in said measurement solution, the appearance of the desilylated against compound or the disappearance of the silylated organic compound, which takes place if fluoride or hydrogen fluoride is present in the sample. The method enables the presence of hydrogen fluoride or of fluorine to be detected very easily and expediently at concentrations of 10.sup.-2 l of HF/10.sup.6 l of air (10 ppb) or else of 0.5 to 1 .mu.g/ml of HF in solution. The kit of the present invention comprises the components which are required for implementing this method. The method of the invention makes it possible to detect fluorine at concentrations of the order of 0.001 .mu.g/ml.