On 29 November 1979 Viehoff became member of the European Parliament when she succeeded Anne Vondeling. For her first four years in the Parliament she was member of the Committee on Youth, Culture, Education, Information and Sport. Between 1984 and 1989 she was member of the Committee on Energy, Research and Technology. And for the largest part of her time in Parliament she was also part of the Delegation for relations with Japan. During her time as MEP Viehoff was supportive of biotechnology as a socially steerable technology. In February 1987 she presented the report Biotechnology in Europe and the need for an integrated policy, the report was adopted by the European Parliament. In February 1989 Viehoff asked the European Commission whether it was going to discipline former Dutch Prime Minister Dries van Agt for comments he made regarding the Dutch delegation to the funeral of Japanese Emperor Dries van Agt. She found his comments towards the Dutch government denigratory. Viehoff's term in the European Parliament ended on 24 July 1989.
