Professor Hopwood is distinguished for his contributions to knowledge of the lysosome and the delineation of inborn errors of metabolism within this organelle. These errors result in the lysosomal storage diseases that include the mucopolysaccharidoses. Hopwood’s contribution has included the purification of the enzymes, the cloning of six of the genes that encode them, the production of recombinant enzymes for each of these and the development of procedures for their use for the treatment of patients with disease. Cloning of the genes revolutionised the ability to provide accurate diagnostics and enabled therapies to be developed. Thus far one of these recombinant enzymes has now received FDA approval as a drug for the effective treatment of a mucopolysaccharidosis and another such approval is imminent. No other Australian scientist has two FDA approved drugs as a direct outcome of his work.