THE HISTORY OF SAFEGUARDS DEVELOPMENT SHOWS THAT POTENTIAL THREATS AND RELATED SAFEGUARDS HAVE HITHERTO BEEN ONLY VAGUELY AND INADEQUATELY DEFINED. NONWEAPONS STATES WOULD MOST PROBABLY STEAL TO ACQUIRE A SECRET NUCLEAR ARSENAL OF AT LEAST TWO OR THREE OPERATIONAL DEVICES. EXTENSIVE TECHNICAL AND FINANCIAL RESOURCES WOULD BE NECESSARY TO MAKE WEAPONS FROM THE STOLEN MATERIAL. BECAUSE OF THE LARGE QUANTITIES OF MATERIALS NEEDED OVER A LONG PERIOD OF TIME, MATERIALS BALANCE SYSTEMS SHOULD BE EFFECTIVE AT DETECTING THEFT, WHEREAS, PERSONNEL AND PHYSICAL SECURITY MEASURES ARE OF MINIMAL IMPORTANCE. IN CONTRAST, TERRORISTS WOULD PROBABLY OBTAIN MATERIALS BY HIJACKING OR BOMBING SHIPMENTS, STEAL MATERIALS OR DEVICES FROM A FACILITY, OR TRY TO CONSTRUCT A DEVICE. SINCE TERRORISTS HAVE FEW FINANCIAL OR TECHNICAL RESOURCES COMPARED TO NONWEAPONS STATES, THEY MUST STEAL PLUTONIUM OR HIGHLY ENRICHED URANIUM. PHYSICAL AND PERSONNEL SECURITY SYSTEMS ARE THEREFORE THE MOST IMPORTANT SAFEGUARDS AGAINST TERRORISTS. MATERIAL BALANCE ACCOUNTING SYSTEMS ARE MINIMALLY IMPORTANT. A THIRD TYPE OF POTENTIAL THIEF, ORGANIZED CRIME SYNDICATES, IS DISCUSSED AND DISCOUNTED. ORGANIZED CRIME WOULD STEAL NUCLEAR MATERIALS ONLY FOR GAIN OFFERED BY ONE OF THE OTHER TWO GROUPS. OTHER THREATS OR ILLOGICAL BEHAVIOR BY POTENTIAL DIVERTERS ARE ALSO POSSIBLE. THOSE CONCERNED ABOUT THESE POSSIBILITIES SHOULD EXAMINE THEM LOGICALLY RATHER THAN PROPOSING SAFEGUARDS BASED ON VAGUE GENERALIZATIONS. AUDIENCE DISCUSSION IS INCLUDED. (CFW)