['International guidelines on ethics in biomedical research require that the informed consent of all enrolled participants is obtained. A written document describing the research, the informed consent (IC) document, must be given to all participants by the investigator. Most IC documents are long, containing much information. The aim of the present study was to determine whether the modification of the IC document by a working group or systematic improvement in its lexicosyntactic readability can improve comprehension of the written information given to patients participating in biomedical research.', 'One hundred and fifty-nine patients were randomized to read one of the three versions of the IC document: unchanged document, document modified using systematic improvement of lexicosyntactic readability and document modified by a working group.', 'Neither the improvement in the lexicosyntactic readability, nor the intervention of the working group significantly improved the score of objective comprehension for the subjects included in this study: it was 66.6 (95% confidence interval 64.0, 69.2) for the control group, 68.8 (66.2, 71.4) for the group with the document improved for lexicosyntactic readability and 69.2 (66.0, 72.4) for the group who read the document improved by the working group (P= 0.38).'] Does informed consent document improvement increase patients ' comprehension in biomedical research?