In the early twentieth century, the therapeutic use of radon gas became an accepted medical practice. "Radium emanation" plants were established in many parts of North America to supply radon seeds to physicians. In Canada, these plants were usually established as part of state-supported cancer programs, creating concern among the medical profession, which had hitherto directed cancer treatment. This article explores how issues surrounding the ownership and distribution of radon played out in two Canadian provinces, Manitoba and Ontario. The main focus is an analysis of a computerized database created from more than two thousand radon order forms, dating from 1933 to 1940, preserved in the Archives of Ontario, which reveals interesting information about patients and the uses of radon in the 1930s, as well as discrepancies between policy and practice that illuminate the medical politics of the era. Although the radon seeds were intended for use in the government-supported central cancer clinics, they were widely distributed to practitioners throughout Ontario, and many patients received treatment for noncancerous conditions. These discrepancies are explored in the context of the struggles over cancer policy between the government and the Ontario medical profession. The article also shows how similar conflicts evolved in Manitoba. Finally, the distribution of radon is linked to the public acceptance of medical radiation despite contemporary reports of harm.