Microscale thermophoresis (MST) is a powerful tool to measure the affinities of interactions between proteins. We present here our method for determining the binding of Rab29 GTPase to the LRRK2 (Leucine rich repeat kinase 2) N-terminal Armadillo domain. Work from several labs has shown that Rab29 can recruit LRRK2 to the Golgi, where it normally resides, or to other compartments, when artificially relocalized to another cellular compartment. MST has enabled us to define the precise binding site for Rab GTPases on the LRRK2 Armadillo domain.