This paper examines which type of professional services provided by accounting firms can most effectively utilize human resources in generating revenues. Results indicate that for a given level of human resources, management advisory services (MAS) contribute the most to an accounting firm's revenues. This pattern continues to hold after the passage of the Sarbanes-Oxley Act (Act) despite the restriction on MAS imposed by the Act. In addition, with the increasing emphasis on auditing and certification of internal control services in the post-Act period, accounting firms' employees with CPA designations become significant drivers of accounting firms' productivity.