For several decades, substantial numbers of researchers who have just received their Ph.D.s, particularly in the biological and physical sciences, have taken postdoctoral study/research appointments before entering the regular labor market. Most of these appointments are held in universities or similar research environments (e.g., the National Institutes of Health intramural laboratories). Beginning in the late 1960s, the heretofore gradual growth in the fraction of the Ph.D. cohort entering such postdoctoral work accelerated just as the prospects for securing faculty positionsthe types of jobs to which most postdoctorals had traditionally aspired-began a long-term decline. As Figure 1 shows, the proportion of the cohort entering postdoctoral work immediately after the Ph.D. increased sharply after 1968, from levels that were already substantial. By 1980, this fraction was nearly one-half the new Ph.D. cohort in physics and in chemistry, and exceeded 60% in the biosciences, with even larger proportions in many of the biomedical disciplines. Although the fractions of the cohort were much smaller in other science and engineering fields, growth during the 1970s was steady and considerable. Postdoctoral appointees now represent a sizable fraction of the academic science workforce, and are thought to contribute in important ways to the vitality of the research effort.' And, postdoctoral training is widely held to be associated with increased levels of career research productivity.2 Many scientists and policy analysts have expressed concern, however, about the health of the postdoctoral enterprise. Prior to the boom, postdoctoral appointments had seemed to attract the most promising young scientists and seemed to lead them to productive research careers3; but the changing employment situation in the mid1970s led to discussion about the stability of this pattern. In a 1976 paper, Lee Grodzins advanced the plausible hypothesis that continued weak faculty job markets would lead to a deterioration in the quality of those taking postdoctoral appointments.4 very able student would be less willing to forego attractive job offers from industrial and other employers in order to work for several years as a poorly paid postdoctoral appointee, Grodzins argued, when the postdoctoral stint could no longer promise good prospects of a prestigious faculty position at the end. postdoctoral ranks would tend to become populated by The less promising students, those who do not get the strongest offers from the nonacademic sector, wholel will accept a postdoctoral as the best alternative given the options available, with the hope that a better offer will turn up before the postdoctoral is ended.5 Clearly this is an important concern for the quality of academic science in both the short term and the long. William Zumeta is an Assistant Professor in the Graduate School of Management and Senior Research Associate at the Higher Education Research Institute, University of California, Los Angeles, CA 90024. Work on this project was supported by grants from the National Science Foundation, the Spencer Foundation, the Lilly Endowment, and the Andrew W. Mellon Foundation.