BACKGROUND: Patient participation in research studies is often difficult to achieve, and efforts to increase participation rates fail frequently. Given the paucity of evidence on interventions aimed at improving patient participation, we conducted a randomized trial. OBJECTIVES: The first was to assess the effect of the logo of the funding agency on the willingness to consider participation in a prospective cohort study in general practice. The second objective was to assess the effect of two signatures of senior persons on the participation rate in the study. STUDY DESIGN AND SETTING: Parents of 1-5-year-old children at a 'high risk' of developing asthma received general information with or without the logo of the Netherlands Asthma Foundation (=RCT1). In addition, the detailed information was signed by the director of the Netherlands Asthma Foundation and the professor of the department vs. the junior researcher (=RCT2). RESULTS: One thousand nine hundred and thirty-eight children were randomized (RCT1). In the 'logo arm,' 46.4% parents considered participation compared to 48.8% parents in the control arm, the difference being -2.3 (95% CI from -6.0 to 1.4). Eight hundred and sixty-two children were randomized in RCT2. Fifty percent of the parents in the 'senior signature arm' and 54.4% in the 'junior signature arm' decided to participate (difference -4.4, 95% CI from -12.1 to 3.3). The overall participation rate, after additional telephone calls, was 37%. CONCLUSION: Our findings indicate that emphasizing the support of a funding agency and senior persons does not improve participation rates in a prospective cohort study.