The use of an indexing language in the catalogues of university libraries was evaluated from the perspective of the users, using a sociocognitive approach. The methodology consisted of a diagnostic study of the processing and use of indexes of nine libraries of the UNESP Network, specifically those covering civil engineering, education and dentistry, using the Introspective Verbal Protocol technique in both Individual and Group forms. The purpose of the study was to examine the process of bibliographic search as well as views concerning the performance of the indexing languages in dealing with information retrieval. Individuals participating in the Group Verbal Protocols consisted of heads of libraries, cataloguers, reference librarians, faculty staff (teachers) and students. Those participating in the Individual Verbal Protocols consisted of students in their first and last years of the relevant courses. The study reported on statements issued by the 63 participating individuals who obtained unsatisfactory results using the Subject Headings List of the BIBLIODATA Network, this being the indexing language used by the Brazilian UNESP Libraries Network in retrieving information from the ATHENA Catalogue. Problems were reported with the following aspects of the language: a lack of specialized vocabulary and updating, inconsistencies in the syntactic-semantic structure of headings, and ambiguous headings. The evaluation shows that to enable effective information retrieval in a specialized scientific area, an indexing language needs updating, appropriate specificity and consistency.