The reactivity of a "think aloud" verbal protocol and the veridicality of different retrospective protocols were tested over four dissimilar tasks. Generating a concurrent protocol altered accuracy in two tasks, simple addition and a choice between two gambles, and generally prolonged response times. Such reactivity partially qualifies the dominant theory of protocol generation (Ericsson & Simon, 1984). Retrospective protocols yielded substantial forgetting or fabrication in all tasks, supporting the consensus on the nonveridicality of these methods. It is concluded that protocol validity should be based on an empirical check rather than on theory-based assurances.