Over the last two decades, adrenocorticotropic hormone (ACTH) has re-emerged as a potentially effective therapy for nephrotic syndrome, particularly for patients who have failed more conventional immunosuppressive therapies. The initial experience in Europe using synthetic ACTH in membranous nephropathy led to a randomized trial in which ACTH performed comparably to a combined regimen of steroids and alkylating agents. Observational data from American patients treated with natural ACTH gel for resistant nephrotic syndrome have also been promising. While we await larger clinical trials of ACTH in the nephrotic patient population, we still also await a more precise understanding of how the therapy achieves remission of proteinuria. We discuss a number of possible mechanisms for ACTH's beneficial effects on the inflammation and injury that occurs in nephrotic syndrome.