It is apparent that significant progress has been made in the characterization of gp330 in the years that have elapsed since its initial identification as the nephritogenic antigen of Heymann nephritis. However, there are still many gaps in our knowledge and we do not yet have a full picture of the molecular events leading to the formation of immune deposits in glomerular capillaries. Moreover, we still do not have direct information on the normal function(s) of gp330 and RAP and their trafficking in renal and other epithelia. The availability of the yolk sac and other cell lines that express gp330 and RAP together with the identification of the functional domains of RAP should greatly facilitate experimental studies designed to elucidate these problems. Progress will also be greatly facilitated in the future when the complete amino-acid sequence of gp330 becomes available, making possible further structural studies. It is our hope that new knowledge obtained on the molecular mechanisms of HN will provide insights into the molecular pathogenesis of human membranous nephropathy and will provide a strategy for the design of appropriate treatments to interrupt the process.