BMS-345541 is a highly selective inhibitor of I kappa B kinase that binds at an allosteric site of the enzyme and blocks NF-kappa B-dependent transcription in mice. BMS-345541 was identified as a selective inhibitor of the catalytic subunits of IKK (IKK-2 IC(50) = 0.3 uM, IKK-1 IC(50) = 4 uM). A binding model is proposed in which BMS-345541 binds to similar allosteric sites on IKK-1 and IKK-2, which then affects the active sites of the subunits differently. BMS-345541 was shown to have excellent pharmacokinetics in mice, and peroral administration showed the compound to dose-dependently inhibit the production of serum tumor necrosis factor alpha following intraperitoneal challenge with lipopolysaccharide. BMS-345541 is effective against NF-kappa B activation in mice and represents an important tool for investigating the role of IKK in disease models. BMS-345541 blocks both joint inflammation and destruction in collagen-induced arthritis in mice.