Professor Toth was a Postdoctoral Fellow at Carleton University, Ottawa Canada (1974-76, Prof J.W. ApSimon). He returned to Hungary to work as a Research Associate (1977-82), then Scientific Group Leader (1982-1987) at the Central Research Institute for Chemistry, Hungarian Academy of Science. Professor Toth joined the School of Pharmacy at the University of London in 1987 as a Senior Lecturer and Royal Society sponsored Senior Research Fellow.