Gillian Griffiths is Professor of Experimental Pathology in Oxford. She is distinguished for her work on secretory lysosomes, the secretory organelles used by many cells of the immune system. She has made significant contributions in elucidating the cell biology of cytotoxic T lymphocytes, identifying the molecular basis of protein sorting as well as many of the key proteins required for the secretion of this unusual organelle. She was the first to demonstrate that many of the lytic proteins used by cytotoxic T lymphocytes to destroy virally infected cells use the mannose-6-phosphate receptor to reach the secretory lysosomes. She showed that perforin, the protein required for destruction of the target, is activated by cleavage of a pro-piece revealing a lipid-binding domain, thus providing the first structure-function information about perforin. An important aspect of her work has been the use of human genetic diseases to identify the proteins required for biogenesis and exocytosis of secretory lysosomes. This approach reveals not only the function of the missing proteins, but has also lead to some fascinating new insights in the molecular aspects of these diseases. Professor Griffithis noted the similarities between the lysosomal related organelles used by cells of the immune system and melanocytes and identified the molecular basis of this link by studying an unusual group of human genetic diseases combining immunodeficiency and albinism. Her work has taken advantage of experiments of nature and by studying cells from patients with Chediak-Higashi, Griscelli, and Hermansky-Pudlak syndromes she has identified specific proteins required for exocytosis of secretory lysosomes, and mapped the stage of secretion which is disrupted in these disorders by using high resolution imaging of the secretion at the immunological synapse.