Thiazolidinediones (TZDs) are a group of structurally related PPARγ agonists with anti-diabetic actions in vivo. Rosiglitazone (BRL49653) is a prototypical TZD and has served as a reference compound for this class of PPARγ ligands. Pioglitazone is a closely related TZD which also selectively activates PPARγ-1. Pioglitazone is about one tenth as potent as rosiglitazone, with an EC50 of about 500-600 nM for both human and murine PPARγ. In a transactivation assay using COS-1 cells transfected with full length human PPARα and RXRα, pioglitazone and rosiglitazone exhibit low level activation of PPARα at 1 µM and 5.4- and 4.2-fold activation, respectively, at a concentration of 10 µM.