We have developed a resource-based relative-value scale as an alternative to the system of payment based on charges for physicians' services. Resource inputs by physicians include (1) total work input performed by the physician for each service; (2) practice costs, including malpractice premiums; and (3) the cost of specialty training. These factors were combined to produce a relative-value scale denominated in nonmonetary units. We describe here the process by which the physician's work was defined and estimated. The study asked two questions: What is the physician's work for each service performed? and Can work be estimated reliably and validly? We concluded that a physician's work has four major dimensions: time, mental effort and judgment, technical skill and physical effort, and psychological stress. We found that physicians can rate the relative amount of work of the services within their specialty directly, taking into account all the dimensions of work. Moreover, these ratings are highly reproducible, consistent, and therefore probably valid.