As a percentage of the gross national product, expenditures for health care in the United States are considerably larger than in Canada, even though one in seven Americans is uninsured whereas all Canadians have comprehensive health insurance. Among the sectors of health care, the difference in spending is especially large for physicians' services. In 1985, per capita expenditure was $347 in the United States and only $202 (in U.S. dollars) in Canada, a ratio of 1.72. We undertook a quantitative analysis of this ratio. We found that the higher expenditures per capita in the United States are explained entirely by higher fees; the quantity of physicians' services per capita is actually lower in the United States than in Canada. U.S. fees for procedures are more than three times as high as Canadian fees; the difference in fees for evaluation and management services is about 80 percent. Despite the large difference in fees, physicians' net incomes in the United States are only about one-third higher than in Canada. A parallel analysis of Iowa and Manitoba yielded results similar to those for the United States and Canada, except that physicians' net incomes in Iowa are about 60 percent higher than in Manitoba. Updating the analysis to 1987 on the basis of changes in each country between 1985 and 1987 yielded results similar to those obtained for 1985. We suggest that increased use of physicians' services in Canada may result from universal insurance coverage and from encouragement of use by the larger number of physicians who are paid lower fees per service. U.S. physicians' net income is not increased as much as the higher U.S. fees would predict, probably because of greater overhead expenses and the lower workloads of America's procedure-oriented physicians.