A hepatitis B epidemic at the hemodialysis unit of the University Hospital of Lund, Sweden, occurred in 1968-71. Since then all patients on regular hemodialysis have been tested with regard to hepatitis B. 196 patients were followed for more than 6 months (5 for more than 10 yr). 50 patients (26 males/24 females) became HBsAg-positive. The majority, 40 (25/15), never lost their HBsAg during the observation period. 35 of these chronic HBsAg; carriers were also chronic HBeAg carriers. 10/50 HBsAg-positive patients lost their HbsAg; females in much higher frequency than men. Six HBsAg-negative patients developed anti-HBs and anti-HBc. The highly infectious carriers constituted a continuous source of infection. Nevertheless, it was possible to keep the spread of infection under control in the unit. The most effective precaution from spread to the staff is probably protective gloves during all handling of patients. As regards the patients the most important measure was the introduction of separate units for HBsAG-positive and HBsAg-negative patients.