The goal of the Resource-Based Relative Value Scale is to measure the resource costs of physicians' services, or, more centrally, the physicians' total work. This article describes the estimation of relative values for physicians' work before and after the performance of a service (preservice and postservice work). For methodological and practical reasons, we could not obtain direct ratings of preservice and postservice work except for a few services. We therefore developed a systematic process to estimate preservice and postservice time and rate of work per unit of time. Then time and work per unit of time were multiplied to estimate work. The major finding of our investigation is that preservice and postservice work make up a substantial portion of total work. The typical percentages of total work accounted for by preservice and postservice work range from 26% and 33% for imaging services and evaluation and management services, respectively, to 46% for invasive services performed in a hospital inpatient setting.