Back to top Who Can Participate People who wish to enroll in clinical trials often must meet the following requirements. Each study also will have its own additional requirements: The patient should reside close to the research facility (usually within 150 miles). The patient usually must have a specific diagnosis. The patient must meet the study guidelines relating to age, sex, level of disability, and duration of disease. The patient usually must be able to understand the possible risks of participating, give consent, and be able and willing to follow study instructions.