Radiation exposures due to patient sources, a pneumatic transport system, and gas lines in a positron emission tomography imaging facility are estimated for heavy clinical work loads. For simple source approximations and estimated study activities and times, exposure rates are computed that are larger than those anticipated in traditional nuclear medical imaging facilities. Measurements of exposure rates indicate that such an approach will result in conservative estimates of exposure by a factor of 1.2-6.3. Exposure rates due to gas lines may be kept at reasonable levels by careful planning of the routing of the line and by using high flow rates and small bore tubing. If reasonable care is taken to maintain the system so that only a limited number of failures occur, the doses due to pneumatic transport system operation are also small. The nonextremity doses to personnel and other individuals not involved in radiotracer preparation are estimated to be highest due to exposure to the patient sources. Shielding for 511 keV photons may help to minimize exposure. Several practical suggestions are given for further reducing exposure to personnel.