A series of free-radical polymerization initiation systems, based on xanthene dyes as the absorbing chromophores [Rose bengal derivative, 3-(3-methylbutoxy)5,7-diiodo-6-fluorone and 3-acetoxy-2,4,5,7-tetraiodo-6-fluorone] and sulfur-containing amino acids as the electron donors, were investigated. The photoredox pair xanthene dye/sulfur-containing amino acid was effectively used for photoinitiation of free-radical polymerization of the mixture composed of poly(ethylene glycol)diacrylate-l% NH4OH (3 : 1). The highest initiating efficiencies were observed for the system composed of methionine derivatives as the electron donor. The mechanism of photoinduced electron transfer between sulfur-containing amino acids and triplet state of xanthene dye was investigated using laser-flash and steady-state photolysis techniques. Based on photochemistry of xanthene dyes, photochemistry of sulfur-containing amino acids, and obtained results, the mechanism describing the major processes occurring during the photoinitiated polymerization by a photoinduced intermolecular electrontransfer process was postulated. © 2005 Wiley Periodicals, Inc.