Deficient N -sulfoglucosamine sulfohydrolase (SGSH) enzyme activity causes mucopolysaccharidosis (MPS) type IIIA. A fluorimetric SGSH activity assay is commonly used to examine patient cells. Here, we modified this method for brain homogenates and define the parameters for assay linearity. SGSH activity was suppressed outside of these parameters. This method will enable the accurate measurement of SGSH activity in MPS IIIA tissues to examine disease pathogenesis and evaluate therapies.