Abstract: Improved cure system for two-part acrylic adhesive compositions comprising, as a first part, a polymerizable composition of a vinyl, especially acrylate or methacrylate, monomer or monomers, optionally a polymer or oligomer, or a polyfunctional methacrylate and a peroxidic catalyst, and a second part, being an activator containing a monosubstituted thiourea, having a heteroatom in the beta or gamma position relative to the nitrogen bearing the substituent. The disclosed catalyst cure system markedly increases the rate or redox initiated polymerization of the acrylate based adhesives, and gives greater on-part life for the activator.