This is a study of the employment of nonphysician providers--nurse practitioners, physician assistants, and certified nurse midwives--in both rural and urban Community and Migrant Health Centers and of factors associated with their employment, based on a 1991 national survey of 383 Centers. Results of the survey suggest that nonphysician providers, in particular nurse practitioners and certified nurse midwives, primarily serve as physician substitutes, and are more likely to be employed by Centers that are larger and have affiliations with nonphysician provider training programs. Rural or urban location is not significantly related to the employment of nonphysician providers after controlling for center size. The fact that rural centers employ fewer nonphysician providers than urban centers can primarily be accounted for by their relatively small size, rather than a lack of interest. These findings demonstrate that the use of nonphysician providers is an important way both to achieve cost containment and improve access to primary care for those residing in medically underserved areas.