After U.S. Senator Everett Dirksen (R-Ill.) died in office in 1969 and Ralph Tyler Smith was appointed to the seat, Stevenson defeated Smith in a 1970 special election by a 58% to 42% margin to fill Dirksen's unexpired term. Stevenson introduced legislation requiring an end to all foreign aid to South Vietnam by June 30, 1975. He authored the International Banking Act, the Stevenson Wydler-Technology Innovation Act and its companion, the Bayh Dole Act, to foster cooperative research, organize national laboratories for technology utilization and commercialization, permit private sector interests in government-funded research. He was the first Chairman of the Senate Ethics Committee charged with implementing a code of ethics he helped draft. Stevenson was also chairman of a Special Senate Committee that reorganized the Senate and served on the Democratic Policy Committee. Inter alia, he also conducted the first in-depth congressional study of terrorism as Chairman of the Subcommittee on the Collection and Production of Intelligence, leading to introduction of the Comprehensive Counter Terrorism Act of 1971 with warnings of "spectacular acts of disruption and destruction" and an amendment that proposed reducing assistance for Israel by $200 million until the president could certify that settlements policies of the newly elected Likud Government of Israel were consistent with U.S. policy. His amendment received seven votes.