This report is a case study of the effectiveness of an occupational health physician's formal recommendation for improving the working environment at a workplace where the employees work on a contract basis. At the business premises, Office B of Company A, where one of the present authors has been appointed as an occupational health physician, some employees have been performing contract work at a Factory Q run by a Company P. Despite dust, organic solvents, and specified chemical substances having been handled in Factory Q for many years, the Company P had not performed any measurements of the working environment, had not installed all the ventilation devices needed for organic solvents and other regulated chemical substances, and had not posted wall-notices with information about the substances handled. Company P had not made use of any occupational health services at Factory Q. Based on a workplace inspection visit report by the former occupational health physician, the site director of Office B requested Company P to make certain improvements, but no measures had been taken. The site director and the occupational health physician then discussed the situation, and notified the top management of Company A about the potential for making a formal recommendation of an occupational health physician. Subsequently, the chief executive officer of Company A sent Company P a document requesting improvement of the working environment based on the report of the occupational health physician. Company P then improved the working environment on that basis.