A countermanding procedure and race model are used to assess separately the effects of experimental factors before and after the "point of no return" in response preparation. The results reveal details about processes that so closely precede the initiation of movement that they cannot be inhibited. These processes appear to be affected by the repetition of stimulus-response pairs, but not by the physical or semantic properties of the stimuli. A model of response preparation is supported in which response inhibition depends upon the outcome of a race between independent excitatory and inhibitory processes, and reaction time is the sum of the durations of at least two stages, separated by the point of no return.