Purpose.To evaluate if marking up heading elements of Web sites improves usability and accessibility. Method.Task completion times and questionnaire responses were collected from sighted and blind users for two kinds of Web sites: sites marked up appropriately with heading elements, and sites with the same visual appearance but with no heading elements marked up. The experiment was carried out with user agents that could navigate through heading elements. Results.1 Heading elements improved usability both for sighted and blind users in terms of significantly reduced task completion time and also higher user satisfaction with the structured site. 2 A significant difference in accessibility i.e., if reduction of task completion time is larger for blind users than sighted users was not observed when heading elements were marked up. The lack of significant effect in this case might have been due to blind users making use of the user-agent's navigation functions to find the target information efficiently when the heading elements were not present. Conclusions.A combination of content with heading elements marked up, user agents with functions that utilise structure markup, and users with sufficient knowledge about user agents functionality, improves usability for both sighted and blind users and may improve accessibility for blind users. © 2009 Informa UK Ltd All rights reserved.