Doctors working through a temp agency is fairly common, and getting more so. According to a survey by Staff Care, spending on temp doctors nationwide has more than doubled since 2001, and the number of days worked by physicians on a temporary basis has grown by 20% from 2006 to 2007. But some say the growing use of temporary doctors is an early sign of a shortage of primary-care physicians. Primary-care doctors are most in demand as temps, and this need is expected to grow as the population ages.