In her research, she focused on antineoplastic PK and PD in children, pharmacogenetics of antileukemia therapy and host- and treatment-related risk factors for secondary malignancies.

[3] In 2007, while serving as Chair of the Pharmaceutical Department, Relling led a study on the impact of inherited polymorphisms on patients with acute lymphoblastic leukaemia.

[4] While serving as Chair of the Pharmaceutical Department at St. Jude Children's Research Hospital, Relling focused on improving drug therapy for childhood leukaemia.

[8] The following year, Relling was the senior author of the "first genome-wide study to demonstrate an inherited genetic basis for racial and ethnic disparities in cancer survival linked Native American ancestry with an increased risk of relapse in young leukemia patients.

"[13] While serving with the National Institutes of Health Pharmacogenomics Research Network (PGRN), Relling received a grant to develop better ways to predict how patients will respond to the drugs they're given.