Initially, the dietitians' role in the Diabetes Control and Complications Trial (DCCT) was specifically defined to include evaluation of potential study volunteers, collection of dietary histories, provision of nutrition education, and participation in team management meetings. As the study progressed, recognition of the importance of adherence to diet in achieving hemoglobin A1c goals and the occurrence of undesirable weight gain in patients assigned randomly to intensive therapy provided an opportunity for dietitians to use their skills intensively and broadly. The need for dietary adherence made DCCT teams aware that dietitians needed to become more active in recruiting and selecting study volunteers and in implementing and evaluating all aspects of intensive diabetes treatment. Increased involvement in these activities allowed dietitians to develop relationships with research patients that were necessary to negotiate treatment goals and improve insights into dietary issues affecting care. Recognition of the importance of dietitians to the DCCT and the empowering nature of the annual meeting of DCCT dietitians fostered continued expansion of the dietitians' role in the clinical centers and in studywide activities such as promotion of dietary adherence, ancillary studies, and publications. Dietitians participating in clinical trials are encouraged to develop their communication and counseling skills, seek out alliances with other team members, and explore opportunities for ancillary research. Such efforts will help to perpetuate this expanded model of the dietitians' role in clinical trials.