A survey of hepatitis B surface antigen (HBSAG) and antibodies against hepatitis C virus (anti-HCV) in 173 patients undergoing hemodialysis in Taiwan revealed that 15 (9%) patients were positive for both HBSAG and anti-HCV, 106 (61%) were positive for anti-HCV alone, and 14 (8%) were positive for HBSAG alone. Most HBSAg positivity was acquired before the onset of hemodialysis. Anti-HCV positivity, however, was mainly acquired via the hemodialysis procedure. Patients with dual markers were younger (43.7 +/- 3.3 years old, p = 0.0274), had the longest period on hemodialysis (6.6 +/- 1.3 years, p < 0.001), and more severe liver dysfunction. When compared with those who were negative for both markers, patients with both HBSAG and anti-HCV had an increased incidence of chronicity (5/15 vs. 2/38; p < 0.05), ultrasonographic cirrhosis (5/15 vs. 1/38; p < 0.05), and clinical decompensation (2/15 vs. 0/38; p < 0.05). Their risk for developing ultrasonographic cirrhosis and clinical decompensation was also greater than that of patients with anti-HCV alone (5/15 vs. 8/106 and 2/15 vs. 2/106; p < 0.05 for both). The presence of HBSAG alone, however, did not increase the incidence of liver dysfunction. The presence of anti-HCV alone was only associated with a greater elevation of serum alanine aminotransferase (44.2 +/- 5.5 vs. 19.1 +/- 2.5 U/l; p < 0.05) and an increased incidence of chronicity (30/106 vs. 2/38; p < 0.05). Our results indicate that a high prevalence of HCV superinfection impose a significant risk on a large population of HBSAG-positive hemodialysis patients in Taiwan. As the coexistence of anti-HCV and HBSAG is associated with more severe liver dysfunction, it is urgent to devise effective methods to prevent HCV circulation in a hemodialysis environment-especially in a hepatitis B virus endemic area such as Taiwan.