The use of diagrams in learning and communication is generally considered efficacious and an important skill to cultivate, especially among science students. At the same time, previous research has revealed many problems in student diagram use, including a lack of spontaneity in such use, but the extent to which these problems persist into the tertiary level had not been investigated. The present study examined science and engineering university students' use of diagrams in note taking to learn information from a written passage, and in a subsequent task of constructing an explanation of that information for another person. The results showed that the students used significantly fewer diagrams in explaining compared to when they were note taking, suggesting that many students may lack awareness of the usefulness of diagrams in effectively communicating information to others. The results also revealed that the students used significantly more diagrams in taking notes from and explaining a passage with higher imageability (i.e. easier to visually imagine) compared to one with lower imageability. Educational implications of the findings are discussed. (Contains 1 table.)