[en] This report describes the scientific progress in, and current status of, life-span studies of the long-term health risks in Beagle dogs of chronic irradiation from internally deposited radionuclides or from an external source. The reporting period for this document is the 2-year period from October 1, 1991 through September 30, 1993. Studies that were initiated at three different laboratories (Inhalation Toxicology Research Institute, ITRI, University of Utah, and Argonne National Laboratory, ANL) are presented here because they are being completed at ITRI. All living dogs in the Utah-initiated studies were transferred to the ITRI facility for the remainder of their life-span observations and measurements in September 1987. This report is the fourth in a series of reports dealing with the current status and progress of both the Utah and ITRI studies. Other life-span studies involving dogs exposed to gamma radiation from an external source were initiated and conducted for many years at ANL. In 1991, the decision was made to discontinue the chronic irradiation of the remaining living dogs and to transfer all remaining dogs to ITRI for care, clinical observations, and pathological observations at death or euthanasia. This report provides the current status of these dogs. Status reports on the Utah and ITRI studies comprise most of this report. The ITRI-related section presents brief statements of project objectives, the general procedures used in these studies, and some study-specific features for each of the 19 studies being conducted with either beta- or alpha-emitting radionuclides. Dose- and effect-modifying factors being addressed in these studies include total dose, dose rate, LET, solubility, nonuniformity of dose, species, age, sex, health status, and mode of exposure. Recent additions to experimental protocols for studies in which dogs are still alive involve the collection and analysis of tumor tissues using currently available molecular biology techniques