An experiment was carried out to investigate whether it is useful to add system information to procedural information in instructional text. It was assumed that readers of instructions construct both a procedural and a system mental model, and that the latter enables the readers to infer possible missing information in procedural instructions. Moreover, it was assumed that system information would increase the cognitive load during reading and practicing, and that it would affect the appreciation of the instructions as well as the self-efficacy of the reader. The participants in the experiment read instructions and practiced with a fictitious machine before performing a number of tasks and answering a questionnaire. The results indicate that system information increased the cognitive load during reading and decreased self-efficacy, while the instructional text with system information was judged as more difficult. The effect on performance is limited: system information leads to faster performance for correctly completed tasks.