Objectives-To study whether linguistic analysis and changes in information leaflets can improve readability and understanding. Design-Randomised, controlled study. Two information leaflets concerned with trials of drugs for conditionsldiseases which are commonly known were modified, and the original was tested against the revised version. Setting-Denmark. Participants-235 persons in the relevant age groups. Main measures-Readability and understanding of contents. Results-Both readability and understanding of contents was improved: readability with regard to both information leaflets and understanding with regard to one of the leaflets. Conclusion-The results show that both readability and understanding can be improved by increased attention to the linguistic features of the information.