Pulse radiolysis has been used to measure directly the absolute rates of oxidation by ferricyanide ion of various radicals produced by OH attack on organic solutes. These include mono, di- and polyhydroxylic compounds, hydroxy acids, polyethylene oxides of molecular weight 200, 6000 and 20 000 and the amino acid serine. Radicals produced by hydrogen abstraction from α carbon atoms in alcohols are oxidized at, or near, diffusion-controlled rates, whereas the reactions are much slower for radicals formed by OH-attack elsewhere. The technique has been used to measure the percentage OH-attack at the α position for a series of straight and branched-chain alcohols. Oxygen competes with ferricyanide for radical oxidation. The data for oxygen-containing solutions fit a simple radical-competition scheme which has been used to measure rates of peroxy-radical formation. These approach diffusion-controlled limits.