Steven DeMello, like many people, uses a smartphone to keep a calendar, take notes, create artful photographs and listen to music. 

Recently, he began using it for a new purpose: to participate in a clinical trial. Three times a day, the retired health-care executive, who is 60 years old and has Parkinson’s disease, performs four tests using an app on his iPhone that records his results and provides feedback to researchers—and to him—on how his Parkinson’s symptoms affect his daily life.

“If I know more about my condition, the better and smarter I will be in managing my own care,” he says.

The app, called mPower, is one of five disease-related apps for clinical trials released in March in connection with Apple Inc. ’s introduction of ResearchKit, a platform where users can track personal health data and participate in health studies. Other apps include My Heart Counts for cardiovascular disease, Asthma Health, GlucoSuccess for diabetes, and Share the Journey, for a study of the aftereffects of treatment for breast cancer.

Together the apps—and patients like Mr. DeMello—offer a glimpse of how the ubiquitous smartphone has the potential to transform medical research. Taking advantage of smartphone features such as accelerometers, gyroscopes and GPS locators, the apps track real-time daily activity and supplement other information on a patient’s condition.

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