A variety of cognitive mechanisms have been proposed to apprehend the maintenance of delusional beliefs, a typical feature of schizophrenia. However, none of these mechanisms takes into account the verbal properties of delusions. An alternative behavioral approach is proposed, which considers delusional beliefs as verbal rules and maintenance of delusions as a form of rule-based insensitivity to changing environmental contingencies. A pilot study is described in which patients formerly presenting with delusional ideas and control participants were exposed in a repeated measures design to three different instructional conditions, instructions, no instructions, and self-instructions, in the context of a non-signaled changing multiple reinforcement schedule. Results suggest that, in the presence of instructions, patients formerly presenting with delusional ideas demonstrate greater insensitivity to changes in schedule contingencies than control participants. While these findings are preliminary, they suggest that rule-based insensitivity to changing environmental contingencies constitutes a new promising way to approach maintenance of delusional beliefs.