A description of free-radical reactions in the solid state is important for some processes causing long-term stability problems of natural and synthetic products. Recent studies revealed that, in the solid state, mercaptooctadecanethiyl radicals, C18H37Scenter dot, do not abstract a hydrogen atom from mercaptooctadecane, C18H37SH, but yield perthiyl radicals, C18H37SScenter dot, Via a net sulfur transfer (Faucitano et al. ChemPhysChem 2005, 6, 1100-1107). Here, we demonstrate that such a sulfur transfer is not a general phenomenon of thiyl-radical reactions in the solid state, providing experimental evidence for a solid-state hydrogen-transfer reaction between a dithiyl radical, generated through the photolysis of trans-4,5-dihydroxy-1,2-dithiacyclohexane (DTTox), and dithiothreitol. The photolysis of crystalline solid deposits of DTTox, yields two isomers of 2,3-dihydroxy-1-mercaptotetrahydrothiophene with a combined quantum yield of Phi(F) = 0.39 +/- 0.02. This quantum yield was increased to Phi(F) = 0.87 +/- 0.13 when the solid deposits contained an additional dithiol, DL-1,4-dimercapto-2,3-butanediol (DTT), at a ratio of DTT/DTTox = 10:1. This increase in quantum yield depended, in part, on the presence of oxygen but was independent of residual moisture in the solid samples. Mechanistically, the formation of 2,3-dihydroxy-1-mercaptotetrahydrothiophene can be rationalized by the H transfer from DTT to a photochemically formed dithiyl radical from DTTox, yielding 2 equiv of monothiyl radicals from DTT, followed by a series of radical transformations.