The effects on cognitive resources of splitting attention between technical illustrations and their descriptors were examined in four experiments with high school students of good to very good reading ability. Experiment 1 looked at the effect of having descriptors incorporated within technical illustrations and found that there was an observable advantage for combined formats over split formats. In Experiments 2, 3 and 4 the combined form of presenting a technical illustration was superior to having the descriptors for the technical illustration in an adjacent key. Attempts to obtain increases in the advantage for the combined format with reinforcement failed to demonstrate any reliable result. These data suggested that the format of technical illustrations which required students to integrate mentally disparate sources of information imposes a heavy cognitive load. It was concluded that the format of technical illustrations was superior when descriptors were contained within the diagram as cognitive resources were not required to integrate the descriptors and the diagram.