The effect of the iodide ions on the rate of the composite reactions of the oscillatory IO3--SO32--Fe-(CN)(6)(4-->) system suggests that the role of the iodate-iodide (Dushman) reaction is small in the composite reaction between IO3- and SO32- (positive feedback pathway), while it appears to be the main route for the IO3--Fe(CN)(6)(4-) reaction (negative feedback). It is found that oscillations in a semibatch reactor are preceded by a long nonoscillatory period during which the pH is about 5. Oscillations start without a nonoscillatory period if iodide is added to the reaction mixture at the beginning. These experiments confirm the role of the Dushman reaction in the negative feedback loop. No preoscillatory period is observed in the analogous BrO3--SO32--Fe(CN)(6)(4-) oscillator in a semibatch reactor. It is also shown that ferricyanide is kinetically important as a consequence of its reaction with sulfite. Modeling of the behavior both in a semibatch configuration and in a CSTR with a set of composite reactions is carried out.