Reaction of one-electron oxidant (Br-2(.-)) with tryptophol (TP) and 5-hydroxytryptophol (HTP) have been studied in aqueous solution in the pH range from 3 to 10, employing nanosecond pulse radiolysis technique and the transients detected by kinetic spectrophotometry. One-electron oxidation of TP has produced an indolyl radical that absorbs in the 300-600 nm region with radical pK(a) = 4.9 +/- 0.2, while the reaction with HTP has produced an indoloxyl radical with lambda max at 420 nm and radical pK(a) < 3. Hydroxyl radicals ((OH)-O-.) react with these two compounds producing (OH)-O-. radical adducts that undergo water elimination to give one-electron-oxidized indolyl and indoloxyl radical species, respectively. The indoloxyl radicals react with the parent compound to form dimer radicals with an average association constant of (6.7 +/- 0.4) x 104 M-1. No such dimerization is observed with indolyl radical, indicating that the presence. of the 5-hydroxy group markedly alters its ability to form a dimer. A possible explanation behind such a difference in reactivity has been supported with ab initio quantum chemical calculations.