Physician practices, especially the small practices with just one or two physicians that are common in the United States, incur substantial costs in time and labor interacting with multiple insurance plans about claims, coverage, and billing for patient care and prescription drugs. We surveyed physicians and administrators in the province of Ontario, Canada, about time spent interacting with payers and compared the results with a national companion survey in the United States. We estimated physician practices in Ontario spent $22,205 per physician per year interacting with Canada's single-payer agency--just 27 percent of the $82,975 per physician per year spent in the United States. US nursing staff, including medical assistants, spent 20.6 hours per physician per week interacting with health plans--nearly ten times that of their Ontario counterparts. If US physicians had administrative costs similar to those of Ontario physicians, the total savings would be approximately $27.6 billion per year. The results support the opinion shared by many US health care leaders interviewed for this study that interactions between physician practices and health plans could be performed much more efficiently.