While elaborating a test for cholesterol in the cerebro-spinal fluid, 0. H. Boltz (I) observed and investigated a reaction which occurred predominantly in cases of neuro-syphilis, and which he named the acetic anhydride-sulphuric test. To I c.c. of spinal fluid was added 03 c.c. of acetic anhydride, drop by drop, and after mixing the fluids by shaking, [email protected]. of concentrated sulphuric acid was added in drops, and the mixture shaken again. The development of a blue pink or lilac colour characterized a positive reaction. The test has been studied in this country, and it has been claimed that the reaction is positive in almost every case of general paresis, and negative in almost every other type of mental disorder, except certain cases of non-paretic neuro-syphilis. As this constitutes a surprising degree of specificity of an apparently simple chemical reaction for a single disease, I have carried out the reaction in association with the routine tests in a series of cerebro-spinal fluids with a view to ascertaining its value. One hundred and sixty fluids were examined—a comparatively small number on which to base conclusions, but the results will show that the claims previously advanced for the value of the test require considerable modification.