Data from a large sample of nursing homes were used to examine the cross-sectional association between use of agency staff, regular staff, and quality. Agency use data came from a survey conducted in 2003 (N=1071 nursing homes). The agency and regular staff measures were for nurse aides, licensed practical nurses, and registered nurses. We used a single quality factor constructed from the 14 quality measures in Nursing Home Compare. More agency nurse aides resulted in a smaller increase in quality, compared to the use of an equivalent number of regular nurse aides. Agency registered nurse staff were associated with better quality factor scores, especially in the presence of high levels of regular licensed practical nurses. Our results have policy and practice implications, the most significant of which is that agency registered nurses may be beneficial in a wide variety of circumstances, whereas agency nurse aides and licensed practical nurses should be used with caution.