[en] The Intercomparison Studies Program (ISP) for in-vitro bioassay at Oak Ridge National Laboratory (ORNL) has been in place since May 1991. The ISP was originally created to fill a need in the Radiobioassay area at ORNL, specifically in the areas of Quality Control, Quality Assurance, and Performance Testing. In the beginning, this consisted of two or three laboratories working in a pilot intercomparison program. Once it was determined that this could work effectively, the program began to seek additional members to broaden the scope of the effort. The program became formalized with a quarterly report in January 1992. The ISP currently provides cross-check blind/double-blind samples spiked with known amounts of radioactivity to various Department of Energy (DOE) facilities, universities, and private industry organizations throughout the US. These samples can be packaged according to ORNL procedures (ORNL sample bottles, ORNL chain-of-custody forms, tamper seals etc.), for a single blind sample or according to the needs of a particular facility if the double-blind sample mode is to be maintained. In 1998, the customer base was broadened to include European facilities. In January 1993, the whole-body count program was added. This involves each participating facility receiving a block phantom from the ISP and determining a geometry factor using a known standard. At quarterly intervals, each participant receives an unknown sample for analysis. The sample is counted and the data is collected for publication in an annual report. In October 1994, the fecal program was added. This involves spiking an artificial matrix with known amounts of radioactivity. Laboratories receive unknown samples on a quarterly basis. The sample is counted and the data is collected and published in a quarterly report. The ISP maintains archive samples which can be analyzed in the QC laboratory at the request of any participants if a conflict or discrepancy in a sample analysis/result occurs