In a national survey of institutions with federally assured human research protection programs, we obtained workload and other relevant data on their Institutional Review Boards (IRBs) and management organizations. The number of IRBs increased substantially from 1995 to 2005/06 (491 to 2,728 IRBs) with a further increase in 2008 to 3,853 IRBs. Nationally, IRBs reviewed over a quarter million research applications in the year prior to our survey, of which 35% were new applications requiring full committee review. Compared to estimates from 1995, current IRBs review more new and full committee review applications, but the relative percentage of new and full committee applications remained about the same. High volume research institutions have IRBs with a substantially larger per person workload, relative to smaller volume IRBs (i.e., members spent nearly seven times more hours reviewing new applications outside formal committee meetings). Virtually all IRBs included community representatives as members (92%); however, a small number may not be compliant with federal regulations. The present findings suggest the need for research to (a) examine workload and its effects on review quality, research costs, and faculty morale, (b) develop methods for determining optimal fit between IRB workload demands and institutional labor and Address correspondence to: Prof. Joseph A. Catania, College of Health and Human Sciences, Oregon State University, 705 NW Elizabeth Drive, Corvallis,; E-MAIL: catania1951@comcast.net.. Author Contributions. Drs. Catania, Lo, Wolf, Dolcini, Barker, and Pollack were involved in the design and execution of the project, as well as in the evaluation of the data and writing of the manuscript. Ms. Wertlieb co-directed field work, helped to analyze the data, and helped to conceptualize and develop the manuscript. Mr. Henne was responsible for the data collection; he also participated in the design and execution of the project, and reviewed the final manuscript. 1 Tier One has 120 Institutional Review Board Organizations (IORGs) among 100 institutions, i.e., 29 IORGs are "extras." Tier Two has 1,950 IORGs (2,070 total IORGs: 120 Tier One IORGs and 1,950 Tier Two IORGs), of which 99% are in single IORG institutions, or . 99 × 1,950 = 1,930 single IORG institutions. Of the remaining 20 IORGs in Tier Two, these are all represented by institutions with only 2 IORGs, so 20/2 = 10 institutions. Thus, Tier One (100) + Tier Two (1,930 + 10) institutions = 2,040 total institutions. 2 The following data were used in computing hours worked in reviewing new applications.Bell Report: 14.9 hrs/review high-volume IRBs, 7.1 hrs/review low-volume IRBs on "initial" reviews; overall mean hours = 11.0 hrs/ review for new applications. Present Study data: M new applications = 87.8, M committee size = 13.4 members. New applications = (11.0 hrs/review × 87.8 new applications per IRB)/13.9 members = Number of hours spent on review over all IRBs= 69.5 hours per person/year on new applications. Tier One new applications...