Serum HBsAg and anti-HBs were measured by radioimmunoassay in 384 patients with renal disease, admitted from January 1979 to December 1981 and in 167 controls. Among 384 cases of renal disease, 41 cases (10.7%) were positive for HBsAg, while only 8 out of 167 (4.8%) of the controls were positive, a difference which was barely significant (P<0.05). However in 159 biopsy-proven renal disease patients, 28 (17.6%) were positive for HRsAg, a difference which was highly significant when it was compared to the total control group (P<0.005). Seven of thirty-six (19.4%) cases with mesangio-proliferative glomerulonephritis and 9 of 10 (90.0%) cases with membranous nephro-pathy were positive for HBsAg; when these were compared to the total control group the differences were highly significant (P<0.01 and P<0.0001 respective1y). Serum HBsAg was also positive in the other renal diseases and anti-HBs was detected in some of the renal diseases but they were statistically not significant when compared with the non-renal controls. Glomerular deposits of hepatitis B surface antigen were identified in 5 of 8 biopsies in membranous nephropathy. The HBsAg and anti-HBs prevalence rate in the family members of the patients with renal diseases were 34.1% and 29.3% respectively.