Previous research has reported that the Simon effect (a type of stimulus-response [S-R] compatibility effect) and the inhibition of return effect (IOR; a late cuing effect) do not interact. In this brief report, we analyzed published and unpublished experiments that have examined these effects and found that IOR actually increases the Simon effect. This is a remarkable finding because most factors that delay reaction times (as IOR does) actually decrease the Simon effect. We examine this interaction within the context of seven interpretations of the effect that IOR may have on the task-irrelevant S-R code and two interpretations of the effect that IOR may have on the task-relevant S-R code, two components that underlie the Simon effect. The results falsified more than half of these interpretations, thus permitting future investigations to further reduce the number of theoretical alternatives.