A laser flash photolysis/long path absorption technique has been employed to study at 298 K the kinetics of aqueous phase reactions of the SO-4 radical with a number of species commonly found in cloud water. Much lower radical concentrations were employed than in all previous direct studies of SO-4 reaction kinetics. In the zero ionic strength limit, rate coefficients for SO-4 reactions with the anions HSO-3, Cl-, NO-2, HCOO-, and CH-3COO are found to be 7.5¿108, 2.6¿108, 9.8¿108, 1.1¿108, and 3.7¿106 M-1 s-1, respectively. Rate coefficients for SO4 reactions with the neutral species H2O2, CH3OH, HCOOH, and CH3COOH are found to be 1.2¿107, 8.8¿106, 4.6¿105, and 1.4¿104 M-1 s-1, respectively. For many of the reactions studied, agreement with previously reported data is poor. Of particular importance for cloud chemistry is the fact that the SO-4+HSO-3 reaction proceeds more slowly than previously believed, while the SO-4+Cl- reaction is somewhat faster tan previously thought. Incorporation of these results into cloud chemistry models should reduce the calculated effeciency of free radical chain reactions as an oxidation mechanism for S IV. ¿ American Geophysical Union 1989