Dr. James Martenson, Jr. is a Professor of Oncology, Mayo Clinic College of Medicine, and a consultant in the Mayo Clinic Department of Radiation Oncology. He is also the Research Base Chair for the North Central Cancer Treatment Group Radiation Oncology Committee.

Dr. Martenson's principle research efforts involve clinical trials in patients with gastrointestinal cancer and clinical trials of supportive care, particularly in patients receiving radiation therapy. Most of his research is conducted through cooperative groups, particularly the North Central Cancer Treatment Group.