Abstract. We prove a conjecture of J.P. May concerning the nilpotence of elements in ring spectra with power operations, i.e., H∞-ring spectra. Using an explicit nilpotence bound on the torsion elements in K(n)-local H∞-algebras over En, we reduce the conjecture to the nilpotence theorem of Devinatz, Hopkins, and Smith. As corollaries we obtain nilpotence results in various bordism rings including M Spin * and M String * , results about the behavior of the Adams spectral sequence for E∞-ring spectra, and the non-existence of E∞-ring structures on certain complex oriented ring spectra.