A method for assessing the effect of a test compound on LRRK2 in a cell-based system, the method comprising the steps of a) assessing the effect of exposing the cell-based system comprising LRRK2 to the test compound on the phosphorylation state of Ser910 and/or Ser935 of the LRRK2; and/or b) assessing the effect of exposing the cell-based system comprising LRRK2 to the test compound on the binding of the LRRK2 to a 14-3-3 polypeptide. The method may comprise or further comprise the step of assessing the effect of exposing the cell-based system comprising LRRK2 to the test compound on the subcellular location of LRRK2. The method is considered to be useful in assessing the effect of putative LRRK2 inhibitors in cell based systems, including in vivo systems.