RA839 is a noncovalent small molecule binder to Keap1 with a Kd of ～6 μM and selective activator of Nrf2 signaling. RA839 prevents the induction of both inducible nitric-oxide synthase expression and nitric oxide release in response to lipopolysaccharides in macrophages. RA839 is a selective inhibitor of the Keap1/Nrf2 interaction and a useful tool compound to study the biology of Nrf2.