In 1971, he joined the Hospital for Sick Children as a staff geneticist. In 1970, he was appointed scientist and in 1980 became a senior scientist. In 1996, he was appointed senior scientist and director of the Hospital for Sick Children's Research Institute. He also holds the Lombard Insurance Chair in Pediatric Research. His research interests are human molecular genetics, Fanconi anemia, cystic fibrosis and gene cloning and function.
He is part of the team which holds the United States patent for "Methods of detecting cystic fibrosis gene by nucleic acid hybridization" , filed in 1995.
In 1991, he was made an officer of the Order of Canada for "major molecular biological thrust into cystic fibrosis research". In 1992, he was awarded the 125th Anniversary of the Confederation of Canada Medal. In 1994, he was made a fellow of the Royal Society of Canada. He is a fellow of the Canadian Academy of Health Sciences.