To the Editor.— A COMMENTARY by Hein and Ferguson, Cost of Maternity Care in Rural Hospitals (240:2051,1978), is being widely circulated in the rural counties of western Oregon as a conclusive argument against the local Health Systems Agency's concern for small-hospital obstetric cost efficiency. The Hein-Ferguson article is unpersuasive, and a response seems necessary. Focusing on room charges for mother and infant and delivery room fees, the authors conclude that obstetric services are less expensive in small hospitals. But that argument completely ignores the fundamental difference between hospital costs and patient charges. If institutional health service prices consistently reflected the cost of providing each service, then the facile assumption that low patient fees mean cost efficiency would be justified. However, for a number of reasons hospitals often price certain services independently of costs, and patient prices therefore may not be a good measure of the cost of those services