The purpose of the present study is to investigate the role of HBe antigen in the pathogenesis of membranous glomerulonephritis (MGN) in Japanese children. Of 364 children who underwent renal biopsy from 1976 through 1978 in our institution, 11(10 male, 1 female, ages 1 - 14 years) were found to be HBs antigen carriers and comprise the subject of the present study. All of them exhibited some abnormality on a routine urinalysis at one time during the course. Serum HB associated antigens were studied in all. A routine light, fluorescent and electron microscopic study was performed on 14 biopsied specimens from the 11children. In addition, direct immunofluorescence for HBsAg, HBeAg & HBcAg was done in the majority of the specimens. The results are summerized in the table. The 14 specimens were divided into 2 groups depending upon clinical manifestations at the time of renal biopsy (Group A: 9 specimens from 9 children with nephrotic syndrome or heavy proteinuria, Group B: 5 specimens from 4 children with minimal hematuria). All of the Group A specimens showed MGN stage II or III and the Group B showed either minimal changes or MGN stage IV. In all of the 5 Group A specimens studied HBeAg immune complex was present along the glomerular capillary wall, but not present in any of the 4 Group B specimens. However, HBsAg was demonstrable in only one of the 11 specimens tested. At the time of renal biopsy, circulating HBeAg was studied in 8 children (Group A: 4, Group B: 4). It is of interest that 2 of the 4 Group B children were found to have HBe antigenemia. The above data suggests there is a highly significant relationship between glomerular HBeAg immune complex and the development of MGN. We believe that most cases of HB associated nephropathy seen in the Japanese children are HBeAg mediated MGN.