The Mine Safety and Health Administration (MSHA) and the National Institute of Occupational Safety and Health (NIOSH) conduct a respirator certification program. NIOSH, as the active participant in the program, receives the reports of problems with certified respirators. The process by which NIOSH and the manufacturer resolve the problem is described. Preliminary activities involve entering the available information on a computer disc and seeking additional necessary information. Each received problem has a severity classification assigned to it, ranging from A for problems that may cause immediate death or injury to the respirator user to D for a problem that has no immediate or future relationship to the health or safety of the user. NIOSH notifies the manufacturer of the problem, and information is exchanged to resolve it as quickly and as accurately as possible. If the manufacturer is handling the problem satisfactorily, no further action is taken by NIOSH; if the manufacturer's response is not satisfactory, NIOSH advises that certification may be revoked. User warnings or notices are issued, identifying the respirators that have the problem, describing the problem, and what must be done to correct the problem. Testing of the respirators is usually done by the manufacturer, and when recalls are necessary NIOSH asks the manufacturer to develop a plan, which NIOSH reviews, and approves, if satisfactory. Some example problems and their resolutions are presented.