Purpose - This paper seeks to report an investigation into the ways in which end-users perceive a thesaurus-enhanced search interface, in particular thesaurus and search interface usability. Design/methodology/approach - Thirty academic users, split between staff and postgraduate students, carrying out real search requests were observed during this study. Users were asked to comment on a range of thesaurus and interface characteristics including: ease of use, ease of learning, ease of browsing and navigation, problems and difficulties encountered while interacting with the system, and the effect of browsing on search term selection. Findings - The results suggest that interface usability is a factor affecting thesaurus browsing/navigation and other information-searching behaviours. Academic staff viewed the function of a thesaurus as being useful for narrowing down a search and providing alternative search terms, while postgraduates stressed the role of the thesaurus for broadening searches and providing new terms. Originality/value - The paper provides an insight into the ways in which end-users make use of and interact with a thesaurus-enhanced search interface. This area is new since previous research has particularly focused on how professional searchers and librarians make use of thesauri and thesaurus-enhanced search interfaces. The research reported here suggests that end-users with varying levels of domain knowledge are able to use thesauri that are integrated into search interfaces. It also provides design implications for search interface developers as well as information professionals who are involved in teaching online searching. (English)