A flow technique involving the use of a multicapillary fast mixer is described, which enables the identification by e.s.r. of intermediates produced in rapid reductions of many solutes by solvated electrons in ammonia. Whilst most compounds ArX (X = Cl, Br, I) produce ArH·^â on a few msec. time-scale, iodo-and p-di-iodo-benzene form the biphenyl radical-anion. The behaviour of fluorine-substituted compounds is complex; 2-fluoropyridine and 3-fluorobenzonitrile are reduced to the corresponding radical-anion, but 2- and 4-fluorobenzonitrile and 2,2â ²-difluorobiphenyl yield either the radical-anion or ArH·â or a mixture of both depending on such factors as the relative concentrations of reactants or delay between the point of mixing and the resonant cavity.