 After qualification as a physician, Grange joined the Research Department at the Middlesex Hospital, where he studied the genus "Mycobacterium" and the diseases it causes in humans and other animals.This followed a stay in Zaire to study the Buruli ulcer.His doctoral thesis was on the classification of certain rapidly growing mycobacteria and led to research on the development of bacteriophage typing of mycobacteria for epidemiology.