DHODH is a validated target for the treatment of autoimmune diseases, like relapsing multiple sclerosis and rheumatoid arthritis,[6] and DHODH inhibitors promote differentiation of acute myeloid leukemic cells thereby reducing the level of leukemia‐initiating cells.[7] Moreover, DHODH inhibitors are promising agents for the treatment of various viral diseases including SARS‐CoV‐2.[8] The CPA identifies DHODH modulation at the site of its action, i. e., in the mitochondria, and can detect DHODH inhibitors that are only weakly active or even inactive in an in vitro DHODH assay. Here, DHODH is linked to rheumatoid arthritis.