Purves was later supported by funds from a Medical Research Council grant for research into thyroid problems, administered by a committee headed by Sir Charles Hercus. Hercus encouraged Purves to take the Medical course, which he did between 1935 and 1941 when he graduated MB/ChB. In 1941 Purves became Principal Research Officer and Director of the New Zealand Medical Research Council's Thyroid Research Department in Dunedin which later became the Endocrinology Research Unit. In 1968 the Unit became the Laboratory of Experimental Endocrinology and Metabolism, and in 1971, The Neuroendocrinology Group. Purves played a leading role in the abolition of thyroid enlargement (goitre) which once disfigured nearly 20% of the population.