In the cobalt(II)-catalysed decomposition of t-butyl hydroperoxide at 25°C in a 5:1 mixture (v/v) of chlorobenzene and dioxane, cobalt 2-ethylhexanoate is more active as a catalyst than the cobalt(II) complexes of a number of 1,3-dicarbonyl compounds. These complexes become deactivated and, in general, a decrease in the acidity of the parent 1,3-dicarbonyl compound lowers the rate of deactivation. This relationship, as well as the high activity of the 2-ethylhexanoate, is consistent with the radical chain decomposition of the hydroperoxide being initiated by a catalytic cycle which involves bridged dicobalt complexes. This cycle differs from the currently accepted Haber and Weiss cycle in that it does not directly generate an alkoxy radical.