The yields of radicals from water decomposition produced in the radiolysis of two types of aqueous solutions, thiocyanate and methyl viologen (MV2+), were determined using proton pulses of 5.2 MeV energy. Aerated thiocyanate solutions in the concentration range of 0.001-0.75 M gave yields of (SCN)(2)(.-), formed from scavenging OH radicals, that were lower than those for high-energy electrons and higher than those for He-4 ions of 21 MeV energy. The (SCN)(2)(.-) yield increased with increasing thiocyanate concentration, but the decay of thiocyanate radicals through intratrack reactions appears to be substantial in proton radiolysis. Methyl viologen radical cations (MV.+) formed by scavenging e,,-, H atoms, and OH radicals were measured in deaerated 0.5 mM MV2+ solutions containing formate. The MV.+ yields agreed with the results of steady-state proton beam radiolysis, which confirms earlier results that this system is a suitable chemical dosimeter for ion beam pulse radiolysis. The yields of MV.+ in deaerated MV2+ solutions containing formate and formate/ tertiary butanol were used to determine the yields of OH radicals and the sum of the e(aq)(-) and H atom yields. Both sets of yields for proton beams were lower than the corresponding ones for high-energy electrons and higher than those for 21 MeV He-4 ions. The predicted hydroxyl radical yields for proton beams increase with increasing scavenging capacity and approach the value found for high-energy electron radiolysis. The sum of the e,,-and H atom yields is about 1.8 molecules/100 eV and nearly independent of the scavenging capacity for OH radical. Intratrack reactions were simulated using a deterministic diffusion kinetic model, and the results qualitatively predict the observed yields in the thiocyanate and the MV2+ solutions.