The main objective of the parent project, Joint Collaborative Committee for Radiation Effects Research (JCCRER) Project 2.3, is the development of a database of Mayak PA workers to use for such purposes as the verification of current dose-effect models for deterministic effects of acute exposure including the acute radiation syndrome or ARS. The pilot research was carried out with DOE support (January 1997) to evaluate the possibility of applying primary clinical and dosimetry data available at FIB-l and Mayak P A to the study of deterministic effects from occupational radiation exposures. During the pilot stage, the clinical- and dosimetry database was created using a stratified random sampling of the Mayak PA workers (1948-1954), and a quality control exercise on the resulting data-base. A report on work at the pilot stage of project 2.3 was submitted for the Nuclear Regulatory Commission on February 29, 1997. The work was accepted, approved of, and funded on January 15, 1998, for the long-term stage of Project 2.3. The first stage of the long-term phase (1st year of work) was to carry out the descriptive analysis of the pilot project database and to verify the existing models of acute radiation syndrome. The next stage of the work (2nd and 3rd years) was to extend the clinical- dosimetry database from the pilot number of 225 to final database of 600 persons. The work on collecting, copying, and inputting clinical data has been completed. The dosimetry, occupational histories, demographic data and vital status have been obtained for all workers. During the period of the NIOSH study Project 2.3 was carrying out work to complete a quality control study of the extended database; to prepare standard samples of the data and a library of Aclean data samples for further analysis; to prepare a final Code book; and, to test mathematical and statistical methods of dose-effect assessment for deterministic effects. Acute Radiation Syndrome. The initial focus of effort on the NIOSH ARS project, a component of Project 2.3, waS to add clinical information concerning the 59 accidentally radiation-exposed workers in the former Soviet Union during 1948 through 1958 to a similar number of accident cases collected in the Western world. The work was funded by a National Institute of Occupational Safety and Health (NIOSH) project led by Dr. Nadezhda Okladnikova (FIB-I) and Drs. Niel Wald and Richard Day (University of Pittsburgh). The new data were to be used to test the triage scheme that had been developed by Thoma and Wald in 1959 to provide clinicians without any special knowledge about radiation effects with early diagnostic and prognostic information about the severity of such injury as a basis for medical management. We found that 22 of the 59 cases had more than one blood count within the first 72 hours after the radiation exposure, a prerequisite for the triage injury classification method to be tested. In view of the rarity of the syndrome, all 59 cases were prepared for further study in Project 2.3 A selection was therefore made of 77 clinical and laboratory items that were of most significance and likely to be on record in most cases. In addition, demographic details, prior medical and radiation history and laboratory data were included in the data extraction questionnaire. A quality assurance study of the data extraction by the US participants revealed a low error rate of 4%. Classification of the 22 cases into 5 injury groups was performed by Dr. Wald using clinical, laboratory and dosimetric information. A test of the ability of radiation-naive physicians to correctly classify the RF cases on the basis of 72 hours of data was completed and analyzed. This led to modification and preliminary retesting of the triage scheme. The improved results warrant further testing of the modified scheme.