Though MD-PhD programs have grown rapidly since their introduction in the mid-1960s, and are widely regarded as fostering excellent young investigators and future leaders in research and academic medicine, the types of research careers their graduates can be expected to pursue have been a point of some confusion. Some regard MD-PhD programs as a flexible approach to scientific training, producing both basic scientists and clinical investigators, while others tend to view these programs as generating either one type of researcher or the other. This range of expectations associated with dual-degree programs and their graduates has perplexed observers over the years and complicated the efforts of planners and policymakers in projecting workforce needs and generating recommendations for research training. To learn more about the research careers of MD-PhDs and how these investigators fit into the larger biomedical research workforce, the authors undertook a review of the types of research proposed by dual-degree and other investigators in 12,116 applications to the National Institutes of Health in 1993 and 1994. In comparing the types of research projects proposed by investigators of various degree types (MDs, MD-PhDs, and PhDs) the authors found that the research interests of the MD-PhDs studied were more closely aligned with the laboratory pursuits of most of their PhD counterparts than with the more clinically-oriented endeavors of those with the MD degree alone. During a time when there are persistent concerns about a shortage of investigators to conduct clinical research and growing fears that America's universities may be producing more PhDs than can be meaningfully employed in the scientific enterprise, the authors' finding indicates a need for future workforce planning to better reflect the respective roles played by MDs, MD-PhDs, and PhDs in biomedical and behavioral research.