Abstract Icons, widely used in computer programs, are part of the Graphical User Interface (GUI). They facilitate computer use regardless of users’ level of expertise. The authors report the results of a study focused on measuring performance of computer users in correctly and quickly associating toolbar icons and the action they represent in GUI. The study aimed to investigate the relationships between the rapidity of icon-function detection by user and user expertise, nature of icon (object or symbol) and context (appropriate, inappropriate, neutral). Findings indicated a scarce variation for different levels of expertise in relation to symbols, but only for icons depicting real-world objects, an overall better performance for objects and no significant response to the context. The discussion suggests future investigations in the field and offers practical considerations for GUI designers.