This study contributes to research investigating the effects of individual differences and online instructional design on learning. Learning performance was compared across three hypertext formats incorporating different navigational aids. The hierarchical map represented the physical structure of the hypertext in one condition, while the network map represented the semantic structure of the hypertext in another condition, and the control group received no map. It was hypothesized that an interaction would be observed between the learners ability to visualize the hypertext structure and the explicit graphical representation of that structure, such that larger differences in knowledge acquisition and disorientation would be found among learners with low visualization ability. The analysis also accounted for individual differences like the need for cognition, prior knowledge, and time on task. The results suggest that the cognitive load associated with orientation within hypertext may be ameliorated by providing a comprehensive hierarchical map to serve as navigational aid for the structure of hypertext content, as opposed to providing a non-hierarchical semantic map or no navigational aid. Despite the differences in disorientation, no significant effect of the hypertext format on learning performance was observed. A discussion of the findings includes considerations of methodological aspects of the study. (Contains 8 notes, 3 tables and 10 figures.)