In this report ten cases of acute radiation syndrome are described resulting from two accidents occurring at the Los Alamos Scientific Laboratory of unique nature involving fissionable material. These cases are described in considerable detail. The report comprises ten sections. This volume, part II of the report, is comprised of sections entitled: (1) the Biological Basis for the Clinical Response seen in the Acute radiation Syndrome, (2) Clinical Signs and Symptoms, (3) Discussion of Hematological Findings, (4) Chemistry of the Blood and Urine, (5) Discussion of Pathological Findings, and (6) Reconsiderations of the Calculated Radiation Doses in Terms of the Observed Biological Response of the Patients. This report was prepared primarily for the clinician who is interested in radiation injuries and therefore emphasis has been placed on the correlation of clinical and pathological changes with the type of cytogenetic change known to be produced by ionizing radiation.