Abstract This paper argues that audit firms achieve competitive advantages through specialization, and that clients purchase audit services from the least cost supplier. Client-auditor realignments thus represent efficient responses to changes in client operations and activities over time. Results obtained from analyzing the financial characteristics and share price performance of corporations that changed auditors between 1973 and 1982 support the view that realignments can generally be attributed to cross-temporal changes in client characteristics and differences in audit firm cost structures.