This paper tests the hypothesis that interest rates on bank commercial loans in the regions of the United States are generated in an integrated national market. The tests — of a joint hypothesis compounded of integration, behavioral models, and the absence of systematic errors in the data — are applied to 60 series of data (short-term and long-term loans in five size classes in six regions). The joint hypothesis is not rejected for five of the six regions and four of the five size classes. The exceptional region is the Southeast; the exceptional loan-size class is $1,000 to $9,000, the smallest in the sample.