When firms borrow from multiple concentrated creditors such as banks they appear to differentiate their allocation of borrowing. In this paper, we put forward hypotheses for this borrowing pattern based on incomplete contract theories and test them using a sample of small U.S. firms. We find that firms with more valuable and more homogeneous assets differentiate borrowing more sharply across concentrated creditors. Moreover, borrowing differentiation is inversely related to restructuring costs and positively related to firms' informational transparency. The results suggest that the structure of credit relationships is used to discipline creditors and entrepreneurs, especially during corporate reorganizations.